Paper products and methods and systems for manufacturing such products

ABSTRACT

Methods of producing cellulosic or lignocellulosic materials for use in papermaking include treating a cellulosic or lignocellulosic dry feedstock having a first average molecular weight with ionizing radiation, and controlling the dose of ionizing radiation such that the average molecular weight of the feedstock is reduced to a predetermined level. A method of producing an irradiated paper product includes treating a paper product including a first carbohydrate-containing material having a first molecular weight with ionizing radiation, and controlling the dose of ionizing radiation so as to provide an irradiated paper product with a second carbohydrate-containing material having a second molecular weight higher than the first molecular weight. Pulp and paper products are produced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation (and claims the benefit of priorityunder 35 U.S.C. § 121) of pending U.S. Ser. No. 15/160,612, filed May20, 2016, which is a divisional (and claims the benefit of priorityunder 35 U.S.C. § 121) of granted U.S. Ser. No. 14/474,859, filed Sep.2, 2014, now U.S. Pat. No. 9,365,981, issued on Jun. 14, 2016, which isa divisional (and claims the benefit of priority under 35 U.S.C. § 121)of granted U.S. Ser. No. 12/768,482, filed Apr. 27, 2010, now U.S. Pat.No. 8,834,676, issued on Sep. 16, 2014, which is a divisional (andclaims the benefit of priority under 35 U.S.C. § 121) of granted U.S.Ser. No. 12/417,707, filed Apr. 3, 2009, now U.S. Pat. No. 7,867,358,issued on Jan. 11, 2011, which claimed priority to U.S. ProvisionalApplication Ser. No. 61/049,391, filed Apr. 30, 2008. The completedisclosure of each of these applications is hereby incorporated byreference herein.

TECHNICAL FIELD

This invention relates to methods and systems for preparing paperproducts, and products produced by such methods and systems.

BACKGROUND

Paper, as that term is used herein, refers to the wide variety ofcellulose-based sheet materials used for writing, printing, packaging,and other applications. Paper may be used, for example, but withoutlimitation, in the following applications: as paper money, bank notes,stock and bond certificates, checks, and the like; in books, magazines,newspapers, and art; for packaging, e.g., paper board, corrugatedcardboard, paper bags, envelopes, wrapping tissue, boxes; in householdproducts such as toilet paper, tissues, paper towels and paper napkins;paper honeycomb, used as a core material in composite materials;building materials; construction paper; disposable clothing; and invarious industrial uses including emery paper, sandpaper, blottingpaper, litmus paper, universal indicator paper, paper chromatography,battery separators, and capacitor dielectrics.

Paper is generally produced by pulping a cellulosic material to form apulp containing cellulosic fibers, amalgamating the cellulosic fibers toform a wet web, and drying the wet web. In the finished paper, thefibers are held together by mechanical interlocking and hydrogenbonding. Pulping may be accomplished in a number of ways, for example:using a chemical process (e.g., the Kraft process), a mechanical process(groundwood), or thermomechanical process (TMP). The amalgamating anddrying steps are generally performed using a high speed paper machine.

The most common source of cellulosic fibers is wood pulp from trees.Pulp is also derived from recovered (“recycled”) paper. Vegetable fibermaterials, such as cotton, hemp, linen, and rice, are also used. Othernon-wood fiber sources include, but are not limited to, sugarcane,bagasse, straw, bamboo, kenaf, jute, flax, and cotton. A wide variety ofsynthetic fibers, such as polypropylene and polyethylene, as well asother ingredients such as inorganic fillers, may be incorporated intopaper as a means for imparting desirable physical properties.

For many applications, it is desirable that paper have high strength andtear resistance, even in very thin sheets, for example, when the paperis used in packaging, in industrial applications, as money, and in otherapplications that require strength and durability. It is also generallydesirable that paper exhibit good printability characteristics, with theparticular characteristics depending to some extent on the printingprocess in which the paper will be used.

SUMMARY

The invention is based, in part, on the discovery that by irradiatingfibrous materials at appropriate levels, the physical characteristics ofthe fibrous material can be favorably altered. For example, themolecular weight, level of crosslinking, grafting sites, and/orfunctional groups of at least the cellulosic portions of the materialscan be altered. Moreover, physical properties such as the tensilestrength and shear strength of the fibrous material can be favorablyaffected. Relatively high doses of ionizing radiation can be used toreduce the molecular weight of at least the cellulosic portions of thefibrous material, assisting with transformation of a fibrous material toa pulp that is suitable for use in papermaking. Relatively lower dosesof ionizing radiation can be used to increase the molecular weight of apaper product, enhancing its tensile strength and other mechanicalproperties. Ionizing radiation can also be used to control thefunctionalization of the fibrous material, i.e., the functional groupsthat are present on or within the material.

In one aspect, the invention features methods of producing a cellulosicor lignocellulosic material for use in papermaking. Some methods includetreating a cellulosic or lignocellulosic dry feedstock having a firstaverage molecular weight with at least 2.5 MRad of ionizing radiation toreduce the average molecular weight of the feedstock to a predeterminedlevel.

Some implementations include one or more of the following features. Thepredetermined level is selected so that the treated feedstock issuitable for use as, or in forming, a pulp in a papermaking process. Themethods further include subjecting the treated feedstock to a pulpingprocess. The methods further include subjecting the treated feedstock toa mechanical disintegrating process. The methods can further includeapplying acoustic energy to the treated feedstock.

In some embodiments, the feedstock can include wood chips, and the doseof ionizing radiation can be about 2.5 to about 10 MRad. Treating caninclude irradiating with gamma radiation and/or irradiating withelectron beam radiation. In certain embodiments, the electrons in theelectron beam can have an energy of at least 0.25 MeV.

In another aspect, the invention features methods of making anirradiated paper product. Some methods include treating a paper productincluding a first carbohydrate-containing material having a firstmolecular weight with ionizing radiation to provide an irradiated paperproduct including a second carbohydrate-containing material having asecond molecular weight higher than the first molecular weight.

Some implementations include one or more of the following features. Thedose of ionizing radiation can be at least 0.10 MRad, e.g., at least0.25 MRad. The dose of ionizing radiation can be controlled to a levelof about 0.25 to about 5 MRad. Treating can include irradiating withgamma radiation, and/or with electron beam radiation. Electrons in theelectron beam can have an energy of at least 0.25 MeV, e.g., from about0.25 MeV to about 7.5 MeV. The methods can further include quenching thetreated paper product. For example, quenching can be performed in thepresence of a gas selected to react with radicals present in the treatedpaper product.

In yet a further aspect, the invention features methods of making anirradiated paper product that include treating a carbohydrate-containingpulp material with ionizing radiation such that the average molecularweight of the carbohydrate-containing pulp material is increased.

Some implementations of these methods can include one or more of thefollowing features. Treating can occur during formation of the paperproduct. Forming can include amalgamating the pulp material into a wetpaper web. Treating can be performed on the wet paper web or prior toformation of the wet paper web. Forming can further include drying thewet paper web, and treating can occur after drying.

In a further aspect, the invention features a paper, the papercomprising an irradiated lignocellulosic material, wherein theirradiated lignocellulosic material includes at least about 2 percent byweight lignin, such as at least about 2.5, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0or at least about 10.0 percent by weight lignin.

In some cases, the irradiated lignocellulosic material includescrosslinks, and the crosslinks occur in at least the lignin portion ofthe irradiated lignocellulosic material.

The invention also features a method of making a paper, the methodincluding combining a cellulosic or lignocellulosic material with ligninand forming a paper from the combination.

In some cases the cellulosic or lignocellulosic material has beenirradiated, and/or the combination is irradiated and then formed into apaper, and/or the formed paper is irradiated.

The invention also features pulp and paper products formed byirradiating cellulosic and lignocellulosic materials, e.g., using themethods described herein.

In one aspect, the invention features pulp materials including a treatedcellulosic or lignocellulosic fibrous material having an averagemolecular weight of less than 500,000 and containing functional groupsnot present in a naturally occurring cellulosic or lignocellulosicfibrous materials from which the treated material was obtained. Forexample, in some embodiments, the functional groups include enol groupsand/or carboxylic acid groups or salts or esters thereof. The functionalgroups can also be selected from the group consisting of aldehydegroups, nitroso groups, nitrile groups, nitro groups, ketone groups,amino groups, alkyl amino groups, alkyl groups, chloroalkyl groups,chlorofluoroalkyl groups, and carboxylic acid groups. In some cases thenaturally occurring cellulosic or lignocellulosic fibrous materials caninclude wood chips.

In another aspect, the invention features paper products that include atreated cellulosic or lignocellulosic fibrous material, the treatedcellulosic or lignocellulosic fibrous material containing functionalgroups not present in a naturally occurring cellulosic orlignocellulosic fibrous material from which the treated material wasobtained.

The cellulosic or lignocellulosic material can be selected from thegroup consisting of paper waste, wood, particle board, sawdust, silage,grasses, rice hulls, bagasse, cotton, jute, hemp, flax, bamboo, sisal,abaca, straw, corn cobs, corn stover, switchgrass, alfalfa, hay, ricehulls, coconut hair, cotton, seaweed, algae, and mixtures thereof.

The term “dry feedstock” as used herein refers to a feedstock (e.g.,woodchips or other cellulosic or lignocellulosic fibrous material)having a moisture content of less than 25%.

The full disclosures of each of the following U.S. patent applications,which are being filed concurrently herewith, are hereby incorporated byreference herein: U.S. patent application Ser. No. 12/417,720, issued asU.S. Pat. No. 7,846,295 on Dec. 7, 2010, U.S. patent application Ser.No. 12/417,699, issued as U.S. Pat. No. 7,931,784 on Apr. 26, 2011, U.S.patent application Ser. No. 12/417,840 issued as U.S. Pat. No. 8,236,535on Aug. 7, 2012, U.S. patent application Ser. No. 12/417,731, U.S.patent application Ser. No. 12/417,900, U.S. patent application Ser. No.12/417,880 issued as U.S. Pat. No. 8,212,087 on Jul. 3, 2012, U.S.patent application Ser. No. 12/417,723, U.S. patent application Ser. No.12/417,786 issued as U.S. Pat. No. 8,025,098 on Sep. 27, 2011, and U.S.patent application Ser. No. 12/417,904 issued as U.S. Pat. No. 7,867,359on Jan. 11, 2011.

In any of the methods disclosed herein, radiation may be applied from adevice that is in a vault.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods andmaterials are described below. All mentioned publications, patentapplications, patents, and other references are incorporated herein byreference in their entirety. In case of conflict, the presentspecification, including definitions, will control. In addition, thematerials, methods and examples are illustrative only and not intendedto be limiting.

Other features and advantages of the invention will be apparent from thefollowing detailed description, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a diagrammatic view of a pulping system. FIG. 1B is adiagrammatic view of the pretreatment subsystem of the pulping systemshown in FIG. 1A.

FIG. 2 is a diagrammatic view of a paper making system.

FIG. 3 is a diagram that illustrates changing a molecular and/or asupramolecular structure of a fibrous material.

FIG. 4 is a perspective, cut-away view of a gamma irradiator housed in aconcrete vault.

FIG. 5 is an enlarged perspective view of region, R, of FIG. 4.

FIG. 6 is a schematic diagram of a DC accelerator.

FIG. 7 is a schematic view of a system for sonicating a process streamof cellulosic material in a liquid medium.

FIG. 8 is a schematic view of a sonicator having two transducers coupledto a single horn.

FIG. 9 is a schematic cross-sectional side view of a hybrid electronbeam/sonication device.

FIG. 10 is a schematic diagram of a field ionization source.

FIG. 11 is a schematic diagram of an electrostatic ion separator.

FIG. 12 is a schematic diagram of a field ionization generator.

FIG. 13 is a schematic diagram of a thermionic emission source.

FIG. 14 is a schematic diagram of a microwave discharge ion source.

FIG. 15 is a schematic diagram of a recirculating accelerator.

FIG. 16 is a schematic diagram of a static accelerator.

FIG. 17 is a schematic diagram of a dynamic linear accelerator.

FIG. 18 is a schematic diagram of a van de Graaff accelerator.

FIG. 19 is a schematic diagram of a folded tandem accelerator.

DETAILED DESCRIPTION

As discussed above, the invention is based, in part, on the discoverythat by irradiating fibrous materials, i.e., cellulosic andlignocellulosic materials, at appropriate levels, the molecularstructure of at least a cellulosic portion of the fibrous material canbe changed. For example, the change in molecular structure can include achange in any one or more of an average molecular weight, averagecrystallinity, surface area, polymerization, porosity, branching,grafting, and domain size of the cellulosic portion. These changes inmolecular structure can in turn result in favorable alterations of thephysical characteristics exhibited by the fibrous materials. Moreover,the functional groups of the fibrous material can be favorably altered.

For example, the following properties can be increased by 10, 20, 30,40, 50, 75, or even 100% relative to the same properties prior toirradiation:

TAPPI T494 om-06 Tensile Properties of Paper and Paperboard (UsingConstant Rate of Elongation Apparatus), including tensile strength andbreaking length;

TAPPI Method T 414 om-04 Internal tearing resistance of paper(Elmendorf-type Method);

TAPPI Method T 403 om-02 Bursting strength of paper; and

TAPPI Method T 451 cm-84 Flexural properties of paper (Clark Stiffness).

Various cellulosic and lignocellulosic materials, their uses, andapplications have been described in U.S. Pat. Nos. 7,307,108, 7,074,918,6,448,307, 6,258,876, 6,207,729, 5,973,035 and 5,952,105; and in variouspatent applications, including “FIBROUS MATERIALS AND COMPOSITES,”PCT/US2006/010648, filed on Mar. 23, 2006, and “FIBROUS MATERIALS ANDCOMPOSITES,” U.S. Patent Application Publication No. 2007/0045456. Theaforementioned documents are all incorporated by reference herein intheir entireties. The cellulosic or lignocellulosic material caninclude, for example, paper waste, wood, particle board, sawdust,silage, grasses, rice hulls, bagasse, cotton, jute, hemp, flax, bamboo,sisal, abaca, straw, corn cobs, corn stover, switchgrass, alfalfa, hay,rice hulls, coconut hair, cotton, seaweed, algae, and mixtures thereof.

Relatively high doses of ionizing radiation can be used to reduce themolecular weight of the fibrous material, assisting with transformationof fibrous material to pulp that is suitable for use in papermaking.Thus, irradiation can be used to pre-treat a feedstock and thusfacilitate a chemical, mechanical, or thermo-mechanical pulping process,or in some cases can be used to replace at least a portion of aconventional pulping process. Relatively high doses can also be appliedto selected areas of a paper product or a precursor (e.g., a wet paperweb) to form predetermined regions in which the paper is weakened, e.g.,to create tear zones.

Relatively lower doses of ionizing radiation can be applied, at one ormore stages of a papermaking process and/or to a finished paper product,to increase the molecular weight and the level of crosslinking of apaper product.

Ionizing radiation can also be used to control the functionalization ofthe fibrous material, i.e., the functional groups that are present on orwithin the material, which can increase solubility and/or dispersibilityduring pulping, and can favorably affect the surface properties of apaper product, e.g., the receptivity of the surface to coatings, inksand dyes.

Each of these processes will be discussed in detail below.

The irradiating steps discussed above can be combined in many ways. Someexamples of processes including irradiation include the following:

(a) Irradiating only with a high dose of ionizing radiation, to reducemolecular weight and facilitate pulping. Irradiation can be performedprior to or during pulping.

(b) Irradiating only with a low dose of ionizing radiation, to increasemolecular weight, and pulping conventionally. Irradiation can beperformed at any stage of the papermaking process, or on the finishedpaper.

(c) Irradiating with a high dose of ionizing radiation, to break downmolecular weight and facilitate pulping, followed by irradiation with alow dose of radiation, to increase molecular weight.

(d) Irradiating under conditions that favorably alter the functionalgroups present in the material. This can be accomplished during one ofthe steps discussed above, or as a separate step, as will be discussedin detail below.

(e) Irradiating selected areas of paper or a paper precursor with arelatively high dose of radiation to form predetermined weakened areas.This step can be performed alone, or in combination with any of thesteps discussed in (a)-(d) above.

(f) Irradiating multiple times to achieve a given final dose, e.g.,delivering a dose of 1 MRad repeated 10 times, to provide a final doseof 10 MRad. This may prevent overheating of the irradiated material,particularly if the material is cooled between doses.

Irradiating to Reduce Molecular Weight

Ionizing radiation can be applied to a cellulosic or lignocellulosicfibrous material that is suitable for use in making paper (e.g., woodchips) prior to or during pulping, at a dose that is sufficient toconvert the starting material to pulp. In other words, irradiation witha dose of ionizing radiation that is selected to convert or to aid inconverting the starting material to pulp can be used in place ofconventional pulping processes such as chemical, mechanical, andthermomechanical pulping.

In this case, the dose is selected so that the molecular weight of thestarting material is reduced to an extent similar to the extent by whichmolecular weight is reduced by conventional pulping. For example, in thecase of converting wood chips to pulp, the dose would generally beselected to reduce the molecular weight from the starting molecularweight (1 million or greater) to about 20,000 to 500,000. The optimaldose will depend on the feedstock used, but will generally be in therange of 10 MRad to 1000 MRad, e.g., 25 MRad to 500 MRad, forconventional paper feedstocks such as wood-based materials.

Advantageously, in some implementations it is not necessary to removelignin from the pulp, as is conventionally done during the pulpingprocess. This is the case, for example, if the paper is irradiated witha low, molecular weight increasing, dose of ionizing radiation during orafter the paper making process, as will be discussed below. In thiscase, the residual lignin may actually be useful, as the lignin acts asa filler, effectively reducing the amount of cellulosic material needed,and may be cross-linked by the low dose radiation.

In other implementations, instead of replacing conventional pulping withirradiation, ionizing radiation can be applied prior to or during aconventional pulping process, to facilitate or enhance the pulpingprocess. For example, wood chips can be irradiated with a relativelyhigh dose of ionizing radiation prior to the start of the pulpingprocess. If desired, after irradiation, the wood chips can be subjectedto a mechanical process prior to chemical pulping, such as furtherchipping, shearing, or pulverizing. Irradiating and, optionally,mechanically pulping of the irradiated feedstock, can initiate breakdownof the feedstock, in some cases allowing chemical pulping to beperformed under less harsh conditions, e.g., using fewer chemicals, lessenergy, and/or less water.

Ionizing radiation can also be used in a paper recycling process, tore-pulp waste paper for use as starting material in recycled paperproduction. In this case, the dose of ionizing radiation delivered isselected to be sufficient to break down the hydrogen and mechanicalbonding in the paper without deleteriously affecting the cellulosicand/or lignocellulosic fibers in the paper. The dose of ionizingradiation can, for example, be about 20% to 30% less than the dose usedwhen the starting material is wood chips.

FIG. 1A shows a system 100 for converting cellulosic or lignocellulosicstarting material, wood logs in the example shown, into pulp suitablefor use in papermaking. System 100 includes a feed preparation subsystem110, a pretreatment subsystem 114, a primary process subsystem 118, anda post-processing subsystem 122. Feed preparation subsystem 110 receivesthe starting material in its raw form (e.g., logs), and physicallyprepares the starting material for the downstream processes (e.g.,reduces the size of the material and begins to homogenize the material).In the example shown, this is accomplished by debarking and chipping thelogs. Starting materials with significant cellulosic and lignocellulosiccomponents can have a high average molecular weight and crystallinitythat can make pulping difficult.

Pretreatment subsystem 114 receives feedstock (e.g., wood chips) fromthe feed preparation subsystem 110 and prepares the feedstock for use inprimary production processes by, for example, reducing the averagemolecular weight and crystallinity, and changing the kind and degree offunctionalization of the feedstock. This is accomplished, in the exampleshown, by irradiation with a relatively high dose of ionizing radiation,followed by an inline sonication (acoustic) process. Sonication will bediscussed in detail below. A conveyor belt carries the feedstock fromthe feed preparation subsystem 110 to the pretreatment subsystem 114.

As shown in FIG. 1B, in the pretreatment subsystem 114, the feedstock isirradiated, e.g., using electron beam emitters 492, mixed with water toform a slurry, and subjected to the application of ultrasonic energy. Asdiscussed above, irradiation of the feedstock changes the molecularstructure (e.g., reduces the average molecular weight and thecrystallinity) of the feedstock. Mixing the irradiated feedstock into aslurry and applying ultrasonic energy to the slurry further changes themolecular structure of the feedstock. Application of radiation andsonication in sequence can have synergistic effects in that thecombination of techniques appears to achieve greater changes to themolecular structure (e.g., reduction of the average molecular weight andthe crystallinity) than either technique can efficiently achieve on itsown. Without wishing to be bound by theory, in addition to reducing thepolymerization of the feedstock by breaking intramolecular bonds betweensegments of cellulosic and lignocellulosic components of the feedstock,the irradiation can make the overall physical structure of the feedstockmore brittle. After the brittle feedstock is mixed into a slurry, theapplication of ultrasonic energy further changes the molecular structure(e.g., reduces the average molecular weight and the crystallinity) andalso can reduce the particle size of the feedstock.

The conveyor belt 491 carrying the feedstock into the pretreatmentsubsystem distributes the feedstock into multiple feed streams (e.g.,fifty feed streams), each leading to separate electron beam emitters492. Preferably, the feedstock is irradiated while it is dry. Forexample, the feedstock may have a moisture content of less than 25%,preferably less than 20%, less than 15% or less than 10%. Each feedstream is carried on a separate conveyor belt to an associated electronbeam emitter. Each irradiation feed conveyor belt can be approximatelyone meter wide. Before reaching the electron beam emitter, a localizedvibration can be induced in each conveyor belt to evenly distribute thedry feedstock over the cross-sectional width of the conveyor belt.

Electron beam emitter 492 (e.g., electron beam irradiation devicescommercially available from Titan Corporation, San Diego, Calif.) is, inone example, configured to apply a 100 kilo-Gray dose of electrons at apower of 300 kW. The electron beam emitters are scanning beam deviceswith a sweep width of 1 meter to correspond to the width of the conveyorbelt. In some embodiments, electron beam emitters with large, fixed beamwidths are used. A number of factors, including belt/beam width, desireddose, feedstock density, and power applied, govern the number ofelectron beam emitters required for the plant to process 2,000 tons perday of dry feedstock.

In some embodiments, sonication is omitted from the pretreatment system.In some embodiments, further mechanical processing, e.g., furtherchipping, replaces or is used in addition to sonication.

In some cases, the output of primary process subsystem 118 is directlyuseful as pulp, but in other cases, the output requires furtherprocessing, which is provided by post-processing subsystem 122.Post-processing subsystem 122 provides chemical pulping of the output ofthe primary process subsystem (e.g., pressure cooking and digestion, inthe example shown). If the paper to be produced with the pulp isbleached, for example if the paper is bleached printing paper, ableaching step is performed. This step can be omitted for pulp to beused for unbleached paper. In some embodiments, post-processingsubsystem 122 utilizes other pulping processes, such as thermomechanicalpulping, instead of chemical pulping. As shown, in some casespost-processing subsystem 122 can produce treated water to be recycledfor use as process water in other subsystems, and/or can produceburnable waste that can be used as fuel for boilers producing steamand/or electricity.

Irradiating to Increase Molecular Weight

Relatively low doses of ionizing radiation can crosslink, graft, orotherwise increase the molecular weight of a carbohydrate-containingmaterial, such as a cellulosic or lignocellulosic material (e.g.,cellulose). In some embodiments, the starting number average molecularweight (prior to irradiation) of a paper product or a precursor to apaper product is from about 20,000 to about 500,000, e.g., from about25,000 to about 100,000. The number average molecular weight afterirradiation is greater than the starting number average molecularweight, for example by at least about 10%, 25%, 50%, 75%, 100%, 150%,200%, 300%, or as much as 500%. For example, if the starting numberaverage molecular weight is in the range of about 20,000 to about100,000, the number average molecular weight after irradiation is, insome instances, from about 40,000 to about 200,000.

The new methods can be used to favorably alter properties ofcellulose-based papers by applying radiation at one or more selectedstages of the papermaking process. In some cases, irradiation willimprove the strength and tear resistance of the paper, by increasing thestrength of the cellulosic fibers of which the paper is made. Inaddition, treating the cellulosic material with radiation can sterilizethe material, which may reduce the tendency of the paper to promote thegrowth of mold, mildew of the like. Irradiation is generally performedin a controlled and predetermined manner to provide optimal propertiesfor a particular application, such as strength, by selecting the type ortypes of radiation employed and/or dose or doses of radiation applied.

A low dose of ionizing radiation can be applied to increase molecularweight, e.g., after pulping and before amalgamation of the pulped fibersinto a web; to the wet fiber web; to the paper web during or afterdrying; or to the dried paper web, e.g., before, during, or aftersubsequent processing steps such as sizing, coating, and calendering. Itis generally preferred that radiation be applied to the web when it hasa relatively low moisture content. In the example shown in FIG. 2,irradiation can be performed during drying and finishing, e.g., betweensizing, drying, pressing and calendaring operations, or duringpost-processing, e.g., to the finished paper in roll, slit roll or sheetform.

As noted above, in some embodiments radiation is applied at more thanone point during the manufacturing process. For example, ionizingradiation can be used at a relatively high dose to form or to help formthe pulp, and then later at a relatively lower dose to increase themolecular weight of the fibers in the paper. As will be discussed infurther detail below, radiation can also be applied to the finishedpaper in a manner so as to favorably affect the functional groupspresent within and/or on the surface of the paper. High dose radiationcan be applied to the finished paper at selected areas of the paper webto create locally weakened areas, e.g., to provide tear zones.

As a practical matter, using existing technology, it is generally mostdesirable to integrate the irradiation step into the papermaking processeither after pulping and prior to introduction of the pulp to thepapermaking machine, or after the web has exited the papermakingmachine, typically after drying and sizing. However, as noted above,irradiation may be performed at any desired stage in the process.

If desired, various cross-linking additives can be added to the pulp toenhance cross-linking in response to irradiation. Such additives includematerials that are cross-linkable themselves and materials that willassist with cross-linking. Cross-linking additives include, but are notlimited to, lignin, starch, diacrylates, divinyl compounds, andpolyethylene. In some implementations, such additives are included inconcentrations of about 0.25% to about 2.5%, e.g., about 0.5% to about1.0%.

Irradiating to Affect Material Functional Groups

After treatment with one or more ionizing radiations, such as photonicradiation (e.g., X-rays or gamma-rays), e-beam radiation or irradiationwith particles heavier than electrons that are positively or negativelycharged (e.g., protons or carbon ions), any of thecarbohydrate-containing materials or mixtures described herein becomeionized; that is, they include radicals at levels that are detectable,for example, with an electron spin resonance spectrometer. Afterionization, any material that has been ionized can be quenched to reducethe level of radicals in the ionized material, e.g., such that theradicals are no longer detectable with the electron spin resonancespectrometer. For example, the radicals can be quenched by theapplication of sufficient pressure to the ionized material and/or bycontacting the ionized material with a fluid, such as a gas or liquid,that reacts with (quenches) the radicals. Various gases, for examplenitrogen or oxygen, or liquids, can be used to at least aid in thequenching of the radicals and to functionalize the ionized material withdesired functional groups. Thus, irradiation followed by quenching canbe used to provide pulp or paper with desired functional groups,including, for example, one or more of the following: aldehyde groups,enol groups, nitroso groups, nitrile groups, nitro groups, ketonegroups, amino groups, alkyl amino groups, alkyl groups, chloroalkylgroups, chlorofluoroalkyl groups, and/or carboxylic acid groups. Thesegroups increase the hydrophilicity of the region of the material wherethey are present. In some implementations, the paper web is irradiatedand quenched, before or after processing steps such as coating andcalendering, to affect the functionality within and/or at the surface ofthe paper and thereby affect the ink receptivity and other properties ofthe paper. In other implementations, the paper feedstock is irradiatedwith a relatively high dose of ionizing radiation, to facilitatepulping, and then later quenched to improve the stability of the ionizedmaterial in the pulp.

FIG. 3 illustrates changing a molecular and/or a supramolecularstructure of fibrous material, such as paper feedstock, paper precursor(e.g., a wet paper web), or paper, by pretreating the fibrous materialwith ionizing radiation, such as with electrons or ions of sufficientenergy to ionize the material, to provide a first level of radicals. Asshown in FIG. 3, if the ionized material remains in the atmosphere, itwill be oxidized, e.g., to an extent that carboxylic acid groups aregenerated by reaction with the atmospheric oxygen. In some instances,with some materials, such oxidation is desired, because it can aid infurther breakdown in molecular weight of the carbohydrate-containingmaterial (for example, if irradiation is being used to facilitatepulping). However, since the radicals can “live” for some time afterirradiation, e.g., longer than 1 day, 5 days, 30 days, 3 months, 6months, or even longer than 1 year, material properties can continue tochange over time, which in some instances can be undesirable.

Detecting radicals in irradiated samples by electron spin resonancespectroscopy and radical lifetimes in such samples is discussed inBartolotta et al., Physics in Medicine and Biology, 46 (2001), 461-471and in Bartolotta et al., Radiation Protection Dosimetry, Vol. 84, Nos.1-4, pp. 293-296 (1999). As shown in FIG. 3, the ionized material can bequenched to functionalize and/or to stabilize the ionized material.

In some embodiments, quenching includes application of pressure to theionized material, such as by mechanically deforming the material, e.g.,directly mechanically compressing the material in one, two, or threedimensions, or applying pressure to fluid in which the material isimmersed, e.g., isostatic pressing. In the case of paper that has beenionized, pressure may be applied, e.g., by passing the paper through anip. In such instances, the deformation of the material itself bringsradicals, which are often trapped in crystalline domains, into proximityclose enough for the radicals to recombine, or react with another group.In some instances, pressure is applied together with application ofheat, e.g. a quantity of heat sufficient to elevate the temperature ofthe material to above a melting point or softening point of a componentof the ionized material, such as lignin, cellulose or hemicellulose.Heat can improve molecular mobility in the material, which can aid inquenching of radicals. When pressure is utilized to quench, the pressurecan be greater than about 1000 psi, such as greater than about 1250 psi,1450 psi, 3625 psi, 5075 psi, 7250 psi, 10000 psi, or even greater than15000 psi.

In some embodiments, quenching includes contacting the ionized materialwith fluid, such as liquid or gas, e.g., a gas capable of reacting withthe radicals, such as acetylene or a mixture of acetylene in nitrogen,ethylene, chlorinated ethylenes or chlorofluoroethylenes, propylene ormixtures of these gases. In other particular embodiments, quenchingincludes contacting the ionized material with liquid, e.g., a liquidsoluble in, or at least capable of penetrating into, the ionizedmaterial and reacting with the radicals, such as a diene, such as1,5-cyclooctadiene. In some specific embodiments, the quenching includescontacting the ionized material with an antioxidant, such as Vitamin E.If desired, the material can include an antioxidant dispersed therein,and quenching can come from contacting the antioxidant dispersed in thematerial with the radicals.

Other methods for quenching are possible. For example, any method forquenching radicals in polymeric materials described in Muratoglu et al.,U.S. Patent Publication No. 2008/0067724 and Muratoglu et al., U.S. Pat.No. 7,166,650, the disclosures of which are incorporated herein byreference in their entireties, can be utilized for quenching any ionizedmaterial described herein. Furthermore, any quenching agent (describedas a “sensitizing agent” in the above-noted Muratoglu disclosures)and/or any antioxidant described in either Muratoglu reference, can beutilized to quench any ionized material.

Functionalization can be enhanced by utilizing heavy charged ions, suchas any of the heavier ions described herein. For example, if it isdesired to enhance oxidation, charged oxygen ions can be utilized forthe irradiation. If nitrogen functional groups are desired, nitrogenions or any ion that includes nitrogen can be utilized. Likewise, ifsulfur or phosphorus groups are desired, sulfur or phosphorus ions canbe used in the irradiation.

In some embodiments, after quenching, any of the quenched ionizedmaterials described herein can be further treated with one or morefurther doses of radiation, such as ionizing or non-ionizing radiation,sonication, pyrolysis, and oxidation for additional molecular and/orsupramolecular structure change.

In some embodiments, the fibrous material is irradiated under a blanketof inert gas, e.g., helium or argon, prior to quenching.

The location of the functional groups can be controlled, e.g., byselecting a particular type and dose of ionizing particles. For example,gamma radiation tends to affect the functionality of molecules withinpaper, while electron beam radiation tends to preferentially affect thefunctionality of molecules at the surface.

In some cases, functionalization of the material can occursimultaneously with irradiation, rather than as a result of a separatequenching step. In this case, the type of functional groups and degreeof oxidation can be affected in various ways, for example by controllingthe gas blanketing the material to be irradiated, through which theirradiating beam passes. Suitable gases include nitrogen, oxygen, air,ozone, nitrogen dioxide, sulfur dioxide and chlorine.

In some embodiments, functionalization results in formation of enolgroups in the fibrous material. When the fibrous material is paper, thiscan enhance receptivity of the paper to inks, adhesives, coatings, andthe like, and can provide grafting sites. Enol groups can help breakdown molecular weight, especially in the presence of added base or acid.Thus, the presence of such groups can assist with pulping. In thefinished paper product, generally the pH is close enough to neutral thatthese groups will not cause a deleterious decrease in molecular weight.

Particle Beam Exposure in Fluids

In some cases, the cellulosic or lignocellulosic materials can beexposed to a particle beam in the presence of one or more additionalfluids (e.g., gases and/or liquids). Exposure of a material to aparticle beam in the presence of one or more additional fluids canincrease the efficiency of the treatment.

In some embodiments, the material is exposed to a particle beam in thepresence of a fluid such as air. Particles accelerated in any one ormore of the types of accelerators disclosed herein (or another type ofaccelerator) are coupled out of the accelerator via an output port(e.g., a thin membrane such as a metal foil), pass through a volume ofspace occupied by the fluid, and are then incident on the material. Inaddition to directly treating the material, some of the particlesgenerate additional chemical species by interacting with fluid particles(e.g., ions and/or radicals generated from various constituents of air,such as ozone and oxides of nitrogen). These generated chemical speciescan also interact with the material, and can act as initiators for avariety of different chemical bond-breaking reactions in the material.For example, any oxidant produced can oxidize the material, which canresult in molecular weight reduction.

In certain embodiments, additional fluids can be selectively introducedinto the path of a particle beam before the beam is incident on thematerial. As discussed above, reactions between the particles of thebeam and the particles of the introduced fluids can generate additionalchemical species, which react with the material and can assist infunctionalizing the material, and/or otherwise selectively alteringcertain properties of the material. The one or more additional fluidscan be directed into the path of the beam from a supply tube, forexample. The direction and flow rate of the fluid(s) that is/areintroduced can be selected according to a desired exposure rate and/ordirection to control the efficiency of the overall treatment, includingeffects that result from both particle-based treatment and effects thatare due to the interaction of dynamically generated species from theintroduced fluid with the material. In addition to air, exemplary fluidsthat can be introduced into the ion beam include oxygen, nitrogen, oneor more noble gases, one or more halogens, and hydrogen.

Cooling Irradiated Materials

During treatment of the materials discussed above with ionizingradiation, especially at high dose rates, such as at rates greater then0.15 Mrad per second, e.g., 0.25 Mrad/s, 0.35 Mrad/s, 0.5 Mrad/s, 0.75Mrad/s or even greater than 1 Mrad/sec, the materials can retainsignificant quantities of heat so that the temperature of the materialbecomes elevated. While higher temperatures can, in some embodiments, beadvantageous, e.g., when a faster reaction rate is desired, it isadvantageous to control the heating to retain control over the chemicalreactions initiated by the ionizing radiation, such as crosslinking,chain scission and/or grafting, e.g., to maintain process control.

For example, in one method, the material is irradiated at a firsttemperature with ionizing radiation, such as photons, electrons or ions(e.g., singularly or multiply charged cations or anions), for asufficient time and/or a sufficient dose to elevate the material to asecond temperature higher than the first temperature. The irradiatedmaterial is then cooled to a third temperature below the secondtemperature. If desired, the cooled material can be treated one or moretimes with radiation, e.g., with ionizing radiation. If desired, coolingcan be applied to the material after and/or during each radiationtreatment.

Cooling can in some cases include contacting the material with a fluid,such as a gas, at a temperature below the first or second temperature,such as gaseous nitrogen at or about 77 K. Even water, such as water ata temperature below nominal room temperature (e.g., 25 degrees Celsius)can be utilized in some implementations.

Types of Radiation

The radiation can be provided, e.g., by: 1) heavy charged particles,such as alpha particles; 2) electrons, produced, for example, in betadecay or electron beam accelerators; or 3) electromagnetic radiation,e.g., gamma rays, x-rays or ultraviolet rays. Different forms ofradiation ionize the cellulosic or lignocellulosic material viaparticular interactions, as determined by the energy of the radiation.

Heavy charged particles primarily ionize matter via Coulomb scattering;furthermore, these interactions produce energetic electrons that canfurther ionize matter. Alpha particles are identical to the nucleus of ahelium atom and are produced by alpha decay of various radioactivenuclei, such as isotopes of bismuth, polonium, astatine, radon,francium, radium, several actinides, such as actinium, thorium, uranium,neptunium, curium, californium, americium and plutonium.

Electrons interact via Coulomb scattering and bremsstrahlung radiationproduced by changes in the velocity of electrons. Electrons can beproduced by radioactive nuclei that undergo beta decay, such as isotopesof iodine, cesium, technetium and iridium. Alternatively, an electrongun can be used as an electron source via thermionic emission.

Electromagnetic radiation interacts via three processes: photoelectricabsorption, Compton scattering and pair production. The dominatinginteraction is determined by the energy of incident radiation and theatomic number of the material. The summation of interactionscontributing to the absorbed radiation in cellulosic material can beexpressed by the mass absorption coefficient.

Electromagnetic radiation is subclassified as gamma rays, x-rays,ultraviolet rays, infrared rays, microwaves or radio waves, depending onits wavelength.

For example, gamma radiation can be employed to irradiate the materials.Referring to FIGS. 4 and 5 (an enlarged view of region R), a gammairradiator 10 includes gamma radiation sources 408, e.g. ⁶⁰Co pellets, aworking table 14 for holding the materials to be irradiated and storage16, e.g., made of a plurality iron plates, all of which are housed in aconcrete containment chamber (vault) 20 that includes a maze entranceway22 beyond a lead-lined door 26. Storage 16 defines a plurality ofchannels 30, e.g., sixteen or more channels, allowing the gammaradiation sources to pass through storage on their way proximate theworking table.

In operation, the sample to be irradiated is placed on a working table.The irradiator is configured to deliver the desired dose rate andmonitoring equipment is connected to an experimental block 31. Theoperator then leaves the containment chamber, passing through the mazeentranceway and through the lead-lined door. The operator mans a controlpanel 32, instructing a computer 33 to lift the radiation sources 12into working position using cylinder 36 attached to hydraulic pump 40.

Gamma radiation has the advantage of significant penetration depth intoa variety of materials in the sample. Sources of gamma rays includeradioactive nuclei, such as isotopes of cobalt, calcium, technicium,chromium, gallium, indium, iodine, iron, krypton, samarium, selenium,sodium, thalium and xenon.

Sources of x-rays include electron beam collision with metal targets,such as tungsten or molybdenum or alloys, or compact light sources, suchas those produced commercially by Lyncean Technologies, Inc., of PaloAlto, Calif.

Sources for ultraviolet radiation include deuterium or cadmium lamps.

Sources for infrared radiation include sapphire, zinc or selenide windowceramic lamps.

Sources for microwaves include klystrons, Slevin type RF sources or atombeam sources that employ hydrogen, oxygen or nitrogen gases.

In some embodiments, a beam of electrons is used as the radiationsource. A beam of electrons has the advantages of high dose rates (e.g.,1, 5, or even 10 MRad per second), high throughput, less containment andless confinement equipment. Electrons can also be more efficient atcausing chain scission. In addition, electrons having energies of 4-10MeV can have penetration depths of 5 to 30 mm or more, such as 40 mm.

Electron beams can be generated, e.g., by electrostatic generators,cascade generators, transformer generators, low energy accelerators witha scanning system, low energy accelerators with a linear cathode, linearaccelerators, and pulsed accelerators. Electrons as an ionizingradiation source can be useful, e.g., for relatively thin materials,e.g., less than 0.5 inch, e.g., less than 0.4 inch, 0.3 inch, 0.2 inch,or less than 0.1 inch. In some embodiments, the energy of each electronof the electron beam is from about 0.25 MeV to about 7.5 MeV (millionelectron volts), e.g., from about 0.5 MeV to about 5.0 MeV, or fromabout 0.7 MeV to about 2.0 MeV. Electron beam irradiation devices may beprocured commercially from Ion Beam Applications, Louvain-la-Neuve,Belgium or from Titan Corporation, San Diego, Calif. Typical electronenergies can be 1, 2, 4.5, 7.5, or 10 MeV. Typical electron beamirradiation device power can be 1, 5, 10, 20, 50, 100, 250, or 500 kW.Typical doses may take values of 1, 5, 10, 20, 50, 100, or 200 kGy.

Tradeoffs in considering electron beam irradiation device powerspecifications include operating costs, capital costs, depreciation anddevice footprint. Tradeoffs in considering exposure dose levels ofelectron beam irradiation would be energy costs and environment, safety,and health (ESH) concerns. Generators are typically housed in a vault,e.g., of lead or concrete.

The electron beam irradiation device can produce either a fixed beam ora scanning beam. A scanning beam may be advantageous with large scansweep length and high scan speeds, as this would effectively replace alarge, fixed beam width. Further, available sweep widths of 0.5 m, 1 m,2 m or more are available.

In embodiments in which the irradiating is performed withelectromagnetic radiation, the electromagnetic radiation can have anenergy per photon (in electron volts) of, e.g., greater than 10² eV,e.g., greater than 10³, 10⁴, 10⁵, 10⁶ or even greater than 10⁷ eV. Insome embodiments, the electromagnetic radiation has energy per photon ofbetween 10⁴ and 10⁷, e.g., between 10⁵ and 10⁶ eV. The electromagneticradiation can have a frequency of, e.g., greater than 10¹⁶ hz, greaterthan 10¹⁷ hz, 10¹⁸, 10¹⁹, 10²⁰ or even greater than 10²¹ hz. In someembodiments, the electromagnetic radiation has a frequency of between10¹⁸ and 10²² hz, e.g., between 10¹⁹ to 10²¹ hz.

One type of accelerator that can be used to accelerate ions producedusing the sources discussed above is a Dynamitron® (available, forexample, from Radiation Dynamics Inc., now a unit of IBA,Louvain-la-Neuve, Belgium). A schematic diagram of a Dynamitron®accelerator 1500 is shown in FIG. 6. Accelerator 1500 includes aninjector 1510 (which includes an ion source) and an accelerating column1520 that includes a plurality of annular electrodes 1530. Injector 1510and column 1520 are housed within an enclosure 1540 that is evacuated bya vacuum pump 1600.

Injector 1510 produces a beam of ions 1580, and introduces beam 1580into accelerating column 1520. The annular electrodes 1530 aremaintained at different electric potentials, so that ions areaccelerated as they pass through gaps between the electrodes (e.g., theions are accelerated in the gaps, but not within the electrodes, wherethe electric potentials are uniform). As the ions travel from the top ofcolumn 1520 toward the bottom in FIG. 6, the average speed of the ionsincreases. The spacing between subsequent annular electrodes 1530typically increases, therefore, to accommodate the higher average ionspeed.

After the accelerated ions have traversed the length of column 1520, theaccelerated ion beam 1590 is coupled out of enclosure 1540 throughdelivery tube 1555. The length of delivery tube 1555 is selected topermit adequate shielding (e.g., concrete shielding) to be positionedadjacent to column 1520, isolating the column. After passing throughtube 1555, ion beam 1590 passes through scan magnet 1550. Scan magnet1550, which is controlled by an external logic unit (not shown), cansweep accelerated ion beam 1590 in controlled fashion across atwo-dimensional plane oriented perpendicular to a central axis of column1520. As shown in FIG. 6, ion beam 1590 passes through window 1560(e.g., a metal foil window or screen) and then is directed to impinge onselected regions of a sample 1570 by scan magnet 1550.

In some embodiments, the electric potentials applied to electrodes 1530are static potentials, generated, e.g., by DC potential sources. Incertain embodiments, some or all of the electric potentials applied toelectrodes 1530 are variable potentials generated by variable potentialsources. Suitable variable sources of large electric potentials includeamplified field sources, e.g. such as klystrons. Accordingly, dependingupon the nature of the potentials applied to electrodes 1530,accelerator 1500 can operate in either pulsed or continuous mode.

To achieve a selected accelerated ion energy at the output end of column1520, the length of column 1520 and the potentials applied to electrodes1530 are chosen based on considerations well-known in the art. However,it is notable that to reduce the length of column 1520, multiply-chargedions can be used in place of singly-charged ions. That is, theaccelerating effect of a selected electric potential difference betweentwo electrodes is greater for an ion bearing a charge of magnitude 2 ormore than for an ion bearing a charge of magnitude 1. Thus, an arbitraryion X²⁺ can be accelerated to final energy E over a shorter length thana corresponding arbitrary ion X⁺. Triply- and quadruply-charged ions(e.g., X³⁺ and X⁴⁺) can be accelerated to final energy E over evenshorter distances. Therefore, the length of column 1520 can besignificantly reduced when ion beam 1580 includes primarilymultiply-charged ion species.

To accelerate positively-charged ions, the potential differences betweenelectrodes 1530 of column 1520 are selected so that the direction ofincreasing field strength in FIG. 6 is downward (e.g., toward the bottomof column 1520). Conversely, when accelerator 1500 is used to acceleratenegatively-charged ions, the electric potential differences betweenelectrodes 1530 are reversed in column 1520, and the direction ofincreasing field strength in FIG. 6 is upward (e.g., toward the top ofcolumn 1520). Reconfiguring the electric potentials applied toelectrodes 1530 is a straightforward procedure, so that accelerator 1500can be converted relatively rapidly from accelerating positive ions toaccelerating negative ions, or vice versa. Similarly, accelerator 1500can be converted rapidly from accelerating singly-charged ions toaccelerating multiply-charged ions, and vice versa.

Doses

In some embodiments, the high dose irradiating, to reduce molecularweight (with any radiation source or a combination of sources), isperformed until the material receives a dose of at least 2.5 MRad, e.g.,at least 5.0, 7.5, 10.0, 100, or 500 MRad. In some embodiments, theirradiating is performed until the material receives a dose of between3.0 MRad and 100 MRad, e.g., between 10 MRad and 100 MRad or between 25MRad and 75 MRad. If gamma radiation is used, the dose will generally betowards the higher end of these ranges, while if electron beam radiationis used, the dose may, in some embodiments, be towards the lower end.Dosage rates will also be towards the lower end for some cellulosicmaterials which already have relatively low molecular weight, e.g.recycled paper.

In some embodiments, the low dose irradiating, to increase molecularweight (with any radiation source or a combination of sources), isperformed until the material receives a dose of at least 0.05 MRad,e.g., at least 0.1, 0.25, 1.0, 2.5, or 5.0 MRad. In some embodiments,irradiating is performed until the material receives a dose of between0.1 and 2.5 MRad. Other suitable ranges include between 0.25 MRad and4.0 MRad, between 0.5 MRad and 3.0 MRad, and between 1.0 MRad and 2.5MRad.

The doses discussed above, both high and low, are also suitable forfunctionalization of the material, with the degree of functionalizationgenerally being higher the higher the dose.

In some embodiments, the irradiating is performed at a dose rate ofbetween 5.0 and 1500.0 kilorads/hour, e.g., between 10.0 and 750.0kilorads/hour or between 50.0 and 350.0 kilorads/hours. When highthroughput is desired, e.g., in a high speed papermaking process,radiation can be applied at, e.g., 0.5 to 3.0 MRad/sec, or even faster,using cooling to avoid overheating the irradiated material.

In some embodiments in which coated paper is irradiated, the papercoating includes resin that is cross-linkable, e.g., diacrylate orpolyethylene. As such, the resin crosslinks as thecarbohydrate-containing material is irradiated to increase its molecularweight, which can provide a synergistic effect to optimize the scuffresistance and other surface properties of the paper. In theseembodiments, the dose of radiation is selected to be sufficiently highso as to increase the molecular weight of the cellulosic fibers, i.e.,at least about 0.25 to about 2.5 MRad, depending on the material, whilebeing sufficiently low so as to avoid deleteriously affecting the papercoating. The upper limit on the dose will vary depending on thecomposition of the coating, but in some embodiments the preferred doseis less than about 5 MRad.

In some embodiments, two or more radiation sources are used, such as twoor more ionizing radiations. For example, samples can be treated, in anyorder, with a beam of electrons, followed by gamma radiation and/or UVlight having wavelengths from about 100 nm to about 280 nm. In someembodiments, samples are treated with three ionizing radiation sources,such as a beam of electrons, gamma radiation, and energetic UV light.

Acoustic Energy

Radiation may be used in combination with acoustic energy, e.g., sonicor ultrasonic energy, to improve material throughput and/orcharacteristics, and/or to minimize energy usage. For example, acousticenergy can be used in combination with high dose radiation to enhancethe pulping process.

Referring again to FIG. 1A, in the pretreatment system 114, a startingmaterial that will be used to form the pulp, e.g., wood chips, can besubjected to an inline sonication step using acoustic energy.

FIG. 7 shows a general system in which cellulosic material stream 1210(e.g., feedstock to make pulp) is mixed with water stream 1212 inreservoir 1214 to form process stream 1216. A first pump 1218 drawsprocess stream 1216 from reservoir 1214 and toward flow cell 1224.Ultrasonic transducer 1226 transmits ultrasonic energy into processstream 1216 as the process stream flows through flow cell 1224. A secondpump 1230 draws process stream 1216 from flow cell 1224 and towardsubsequent processing.

Reservoir 1214 includes first intake 1232 and second intake 1234 influid communication with volume 1236. A conveyor (not shown) deliverscellulosic material stream 1210 to reservoir 1214 through first intake1232. Water stream 1212 enters reservoir 1214 through second intake1234. In some embodiments, water stream 1212 enters volume 1236 along atangent establishing swirling flow within volume 1236. In certainembodiments, cellulosic material stream 1210 and water stream 1212 areintroduced into volume 1236 along opposing axes to enhance mixing withinthe volume.

Valve 1238 controls the flow of water stream 1212 through second intake1232 to produce a desired ratio of cellulosic material to water (e.g.,approximately 10% cellulosic material, weight by volume). For example,2000 tons/day of cellulosic material can be combined with 1 million to1.5 million gallons/day, e.g., 1.25 million gallons/day, of water.

Mixing of cellulosic material and water in reservoir 1214 is controlledby the size of volume 1236 and the flow rates of cellulosic material andwater into the volume. In some embodiments, volume 1236 is sized tocreate a minimum mixing residence time for the cellulosic material andwater. For example, when 2000 tons/day of cellulosic material and 1.25million gallons/day of water are flowing through reservoir 1214, volume1236 can be about 32,000 gallons to produce a minimum mixing residencetime of about 15 minutes.

Reservoir 1214 includes a mixer 1240 in fluid communication with volume1236. Mixer 1240 agitates the contents of volume 1236 to dispersecellulosic material throughout the water in the volume. For example,mixer 1240 can be a rotating vane disposed in reservoir 1214. In someembodiments, mixer 1240 disperses the cellulosic material substantiallyuniformly throughout the water.

Reservoir 1214 further includes an exit 1242 in fluid communication withvolume 1236 and process stream 1216. The mixture of cellulosic materialand water in volume 1236 flows out of reservoir 1214 via exit 1242. Exit1242 is arranged near the bottom of reservoir 1214 to allow gravity topull the mixture of cellulosic material and water out of reservoir 1214and into process stream 1216.

First pump 1218 (e.g., any of several recessed impeller vortex pumpsmade by Essco Pumps & Controls, of Los Angeles, Calif.) moves thecontents of process stream 1216 toward flow cell 1224. In someembodiments, first pump 1218 agitates the contents of process stream1216 such that the mixture of cellulosic material and water issubstantially uniform at inlet 1220 of flow cell 1224. For example,first pump 1218 agitates process stream 1216 to create a turbulent flowthat persists along the process stream between the first pump and inlet1220 of flow cell 1224.

Flow cell 1224 includes a reactor volume 1244 in fluid communicationwith inlet 1220 and outlet 1222. In some embodiments, reactor volume1244 is a stainless steel tube capable of withstanding elevatedpressures (e.g., 10 bars). In addition or in the alternative, reactorvolume 1244 defines a rectangular cross section.

Flow cell 1224 further includes a heat exchanger 1246 in thermalcommunication with at least a portion of reactor volume 1244. Coolingfluid 1248 (e.g., water) flows into heat exchanger 1246 and absorbs heatgenerated when process stream 1216 is sonicated in reactor volume 1244.In some embodiments, the flow rate and/or the temperature of coolingfluid 1248 into heat exchanger 1246 is controlled to maintain anapproximately constant temperature in reactor volume 1244. In someembodiments, the temperature of reactor volume 1244 is maintained at 20to 50° C., e.g., 25, 30, 35, 40 or 45° C. Additionally or alternatively,heat transferred to cooling fluid 1248 from reactor volume 1244 can beused in other parts of the overall process.

An adapter section 1226 creates fluid communication between reactorvolume 1244 and booster 1250 coupled (e.g., mechanically coupled using aflange) to ultrasonic transducer 1226. For example, adapter section 1226can include a flange and O-ring assembly arranged to create a leak tightconnection between reactor volume 1244 and booster 1250. In someembodiments, ultrasonic transducer 1226 is a high-powered ultrasonictransducer made by Hielscher Ultrasonics, of Teltow, Germany.

In operation, generator 1252 delivers electricity to ultrasonictransducer 1252. Ultrasonic transducer 1226 includes a piezoelectricelement that converts electrical energy into sound in the ultrasonicrange. In some embodiments, the materials are sonicated using soundhaving a frequency of from about 16 kHz to about 110 kHz, e.g., fromabout 18 kHz to about 75 kHz or from about 20 kHz to about 40 kHz (e.g.,sound having a frequency of 20 kHz to 40 kHz). The ultrasonic energy isdelivered to the working medium through booster 1248. Ultrasonic energytraveling through booster 1248 in reactor volume 1244 creates a seriesof compressions and rarefactions in process stream 1216 with intensitysufficient to create cavitation in process stream 1216. Cavitationdisaggregates the cellulosic material dispersed in process stream 1216.Cavitation also produces free radicals in the water of process stream1216. These free radicals act to further break down the cellulosicmaterial in process stream 1216.

In general, 5 to 4000 MJ/m³, e.g., 10, 25, 50, 100, 250, 500, 750, 1000,2000 or 3000 MJ/m³, of ultrasonic energy is applied to process stream 16flowing at a rate of about 0.2 m³/s (about 3200 gallons/min). Afterexposure to ultrasonic energy in reactor volume 1244, process stream1216 exits flow cell 1224 through outlet 1222. Second pump 1230 movesprocess stream 1216 to subsequent processing (e.g., any of severalrecessed impeller vortex pumps made by Essco Pumps & Controls, LosAngeles, Calif.).

While certain embodiments have been described, other embodiments arepossible.

As an example, while process stream 1216 has been described as a singleflow path, other arrangements are possible. In some embodiments, e.g.,process stream 1216 includes multiple parallel flow paths (e.g., flowingat a rate of 10 gallon/min). In addition or in the alternative, themultiple parallel flow paths of process stream 1216 flow into separateflow cells and are sonicated in parallel (e.g., using a plurality of 16kW ultrasonic transducers).

As another example, while a single ultrasonic transducer 1226 has beendescribed as being coupled to flow cell 1224, other arrangements arepossible. In some embodiments, a plurality of ultrasonic transducers1226 are arranged in flow cell 1224 (e.g., ten ultrasonic transducerscan be arranged in flow cell 1224). In some embodiments, the sound wavesgenerated by each of the plurality of ultrasonic transducers 1226 aretimed (e.g., synchronized out of phase with one another) to enhancecavitation acting upon process stream 1216.

As another example, while a single flow cell 1224 has been described,other arrangements are possible. In some embodiments, second pump 1230moves process stream to a second flow cell where a second booster andultrasonic transducer further sonicate process stream 1216.

As still another example, while reactor volume 1244 has been describedas a closed volume, reactor volume 1244 is open to ambient conditions incertain embodiments. In such embodiments, sonication pretreatment can beperformed substantially simultaneously with other pretreatmenttechniques. For example, ultrasonic energy can be applied to processstream 1216 in reactor volume 1244 while electron beams aresimultaneously introduced into process stream 1216.

As another example, while a flow-through process has been described,other arrangements are possible. In some embodiments, sonication can beperformed in a batch process. For example, a volume can be filled with a10% (weight by volume) mixture of cellulosic material in water andexposed to sound with intensity from about 50 W/cm² to about 600 W/cm²,e.g., from about 75 W/cm² to about 300 W/cm² or from about 95 W/cm² toabout 200 W/cm². Additionally or alternatively, the mixture in thevolume can be sonicated for about 1 hour to about 24 hours, e.g., forabout 1.5 hours to about 12 hours or for about 2 hours to about 10hours. In certain embodiments, the material is sonicated for apre-determined time, and then allowed to stand for a secondpre-determined time before sonicating again.

Referring now to FIG. 8, in some embodiments, two electroacoustictransducers are mechanically coupled to a single horn. As shown, a pairof piezoelectric transducers 60 and 62 is coupled to slotted bar horn 64by respective intermediate coupling horns 70 and 72, the latter alsobeing known as booster horns. The mechanical vibrations provided by thetransducers, responsive to high frequency electrical energy appliedthereto, are transmitted to the respective coupling horns, which may beconstructed to provide a mechanical gain, such as a ratio of 1 to 1.2.The horns are provided with a respective mounting flange 74 and 76 forsupporting the transducer and horn assembly in a stationary housing.

The vibrations transmitted from the transducers through the coupling orbooster horns are coupled to the input surface 78 of the horn and aretransmitted through the horn to the oppositely disposed output surface80, which, during operation, is in forced engagement with a workpiece(not shown) to which the vibrations are applied.

The high frequency electrical energy provided by the power supply 82 isfed to each of the transducers, electrically connected in parallel, viaa balancing transformer 84 and a respective series connected capacitor86 and 90, one capacitor connected in series with the electricalconnection to each of the transducers. The balancing transformer isknown also as “balun” standing for “balancing unit.” The balancingtransformer includes a magnetic core 92 and a pair of identical windings94 and 96, also termed the primary winding and secondary winding,respectively.

In some embodiments, the transducers include commercially availablepiezoelectric transducers, such as Branson Ultrasonics Corporationmodels 105 or 502, each designed for operation at 20 kHz and a maximumpower rating of 3 kW. The energizing voltage for providing maximummotional excursion at the output surface of the transducer is 930 voltrms. The current flow through a transducer may vary between zero and 3.5ampere depending on the load impedance. At 930 volt rms the outputmotion is approximately 20 microns. The maximum difference in terminalvoltage for the same motional amplitude, therefore, can be 186 volt.Such a voltage difference can give rise to large circulating currentsflowing between the transducers. The balancing unit 430 assures abalanced condition by providing equal current flow through thetransducers, hence eliminating the possibility of circulating currents.The wire size of the windings must be selected for the full load currentnoted above and the maximum voltage appearing across a winding input is93 volt.

As an alternative to using ultrasonic energy, high-frequency,rotor-stator devices can be utilized. This type of device produceshigh-shear, microcavitation forces that can disintegrate materials incontact with such forces. Two commercially available high-frequency,rotor-stator dispersion devices are the Supraton™ devices manufacturedby Krupp Industrietechnik GmbH and marketed by Don-Oliver DeutschlandGmbH of Connecticut, and the Dispax™ devices manufactured and marketedby Ika-Works, Inc. of Cincinnati, Ohio. Operation of such amicrocavitation device is discussed in Stuart, U.S. Pat. No. 5,370,999.

While ultrasonic transducer 1226 has been described as including one ormore piezoelectric active elements to create ultrasonic energy, otherarrangements are possible. In some embodiments, ultrasonic transducer1226 includes active elements made of other types of magnetostrictivematerials (e.g., ferrous metals). Design and operation of such ahigh-powered ultrasonic transducer is discussed in Hansen et al., U.S.Pat. No. 6,624,539. In some embodiments, ultrasonic energy istransferred to process stream 16 through an electrohydraulic system.

While ultrasonic transducer 1226 has been described as using theelectromagnetic response of magnetorestrictive materials to produceultrasonic energy, other arrangements are possible. In some embodiments,acoustic energy in the form of an intense shock wave can be applieddirectly to process stream 16 using an underwater spark. In someembodiments, ultrasonic energy is transferred to process stream 16through a thermohydraulic system. For example, acoustic waves of highenergy density can be produced by applying power across an enclosedvolume of electrolyte, thereby heating the enclosed volume and producinga pressure rise that is subsequently transmitted through a soundpropagation medium (e.g., process stream 1216). Design and operation ofsuch a thermohydraulic transducer is discussed in Hartmann et al., U.S.Pat. No. 6,383,152.

In some embodiments, it may be advantageous to combine irradiation andsonication devices into a single hybrid machine. For such a hybridmachine, multiple processes may be performed in close juxtaposition oreven simultaneously, with the benefit of increasing pretreatmentthroughput and potential cost savings.

For example, consider the electron beam irradiation and sonicationprocesses. Each separate process is effective in lowering the meanmolecular weight of cellulosic material by an order of magnitude ormore, and by several orders of magnitude when performed serially.

Both irradiation and sonication processes can be applied using a hybridelectron beam/sonication device as is illustrated in FIG. 8. Hybridelectron beam/sonication device 2500 is pictured above a shallow pool(depth ˜3-5 cm) of a slurry of cellulosic material 2550 dispersed in anaqueous, oxidant medium, such as hydrogen peroxide or carbamideperoxide. Hybrid device 2500 has an energy source 2510, which powersboth electron beam emitter 2540 and sonication horns 2530.

Electron beam emitter 2540 generates electron beams that pass though anelectron beam aiming device 2545 to impact the slurry 2550 containingcellulosic material. The electron beam aiming device can be a scannerthat sweeps a beam over a range of up to about 6 feet in a directionapproximately parallel to the surface of the slurry 2550.

On either side of the electron beam emitter 2540 are sonication horns2530, which deliver ultrasonic wave energy to the slurry 2550. Thesonication horns 2530 end in a detachable endpiece 2535 that is incontact with the slurry 2550.

The sonication horns 2530 are at risk of damage from long-term residualexposure to the electron beam radiation. Thus, the horns can beprotected with a standard shield 2520, e.g., made of lead or aheavy-metal-containing alloy such as Lipowitz metal, which is imperviousto electron beam radiation. Precautions must be taken, however, toensure that the ultrasonic energy is not affected by the presence of theshield. The detachable endpieces 2535, are constructed of the samematerial and attached to the horns 2530, are used to be in contact withthe cellulosic material 2550 and are expected to be damaged.Accordingly, the detachable endpieces 2535 are constructed to be easilyreplaceable.

A further benefit of such a simultaneous electron beam and ultrasoundprocess is that the two processes have complementary results. Withelectron beam irradiation alone, an insufficient dose may result incross-linking of some of the polymers in the cellulosic material, whichlowers the efficiency of the overall depolymerization process. Lowerdoses of electron beam irradiation and/or ultrasound radiation may alsobe used to achieve a similar degree of depolymerization as that achievedusing electron beam irradiation and sonication separately.

An electron beam device can also be combined with one or more ofhigh-frequency, rotor-stator devices, which can be used as analternative to ultrasonic energy devices, and performs a similarfunction.

Further combinations of devices are also possible. For example, anionizing radiation device that produces gamma radiation emitted from,e.g., ⁶⁰Co pellets, can be combined with an electron beam source and/oran ultrasonic wave source. Shielding requirements may be more stringentin this case.

Ion Generation

Various methods may be used for the generation of ions suitable for ionbeams which may be used in treating the cellulosic or lignocellulosicmaterials. After the ions have been generated, they are typicallyaccelerated in one or more of various types of accelerators, and thendirected to impinge on the cellulosic or lignocellulosic materials.

(I) Hydrogen Ions

Hydrogen ions can be generated using a variety of different methods inan ion source. Typically, hydrogen ions are introduced into an ionizingchamber of an ion source, and ions are produced by supplying energy togas molecules. During operation, such chambers can produce large ioncurrents suitable for seeding a downstream ion accelerator.

In some embodiments, hydrogen ions are produced via field ionization ofhydrogen gas. A schematic diagram of a field ionization source is shownin FIG. 10. Field ionization source 1100 includes a chamber 1170 whereionization of gas molecules (e.g., hydrogen gas molecules) occurs. Gasmolecules 1150 enter chamber 1170 by flowing along direction 1155 insupply tube 1120. Field ionization source 1100 includes an ionizationelectrode 1110. During operation, a large potential V_(E) (relative to acommon system ground potential) is applied to electrode 1110. Molecules1150 that circulate within a region adjacent to electrode 1110 areionized by the electric field that results from potential V_(E). Alsoduring operation, an extraction potential V_(X) is applied to extractors1130. The newly-formed ions migrate towards extractors 1130 under theinfluence of the electric fields of potentials V_(E) and V_(X). Ineffect, the newly-formed ions experience repulsive forces relative toionization electrode 1110, and attractive forces relative to extractors1130. As a result, certain of the newly-formed ions enter discharge tube1140, and propagate along direction 1165 under the influence ofpotentials V_(E) and V_(X).

Depending upon the sign of potential V_(E) (relative to the commonground potential), both positively and negatively charged ions can beformed. For example, in some embodiments, a positive potential can beapplied to electrode 1110 and a negative potential can be applied toextractors 1130. Positively charged hydrogen ions (e.g., protons H⁺)that are generated in chamber 1170 are repelled away from electrode 1110and toward extractors 1130. As a result, discharged particle stream 1160includes positively charged hydrogen ions that are transported to aninjector system.

In certain embodiments, a negative potential can be applied to electrode1110 and a positive potential can be applied to extractors 1130.Negatively charged hydrogen ions (e.g., hydride ions H⁻) that aregenerated in chamber 1170 are repelled away from electrode 1110 andtoward extractors 1130. Discharged particle stream 1160 includesnegatively charged hydrogen ions, which are then transported to aninjector system.

In some embodiments, both positive and negative hydrogen ions can beproduced via direct thermal heating of hydrogen gas. For example,hydrogen gas can be directed to enter a heating chamber that isevacuated to remove residual oxygen and other gases. The hydrogen gascan then be heated via a heating element to produce ionic species.Suitable heating elements include, for example, arc dischargeelectrodes, heating filaments, heating coils, and a variety of otherthermal transfer elements.

In certain embodiments, when hydrogen ions are produced via either fieldemission or thermal heating, various hydrogen ion species can beproduced, including both positively and negatively charged ion species,and singly- and multiply-charged ion species. The various ion speciescan be separated from one another via one or more electrostatic and/ormagnetic separators. FIG. 11 shows a schematic diagram of anelectrostatic separator 1175 that is configured to separate a pluralityof hydrogen ion species from one another. Electrostatic separator 1175includes a pair of parallel electrodes 1180 to which a potential Vs isapplied by a voltage source (not shown). Particle stream 1160,propagating in the direction indicated by the arrow, includes a varietyof positively- and negatively-charged, and singly- and multiply-charged,ion species. As the various ion species pass through electrodes 1180,the electric field between the electrodes deflects the ion trajectoriesaccording to the magnitude and sign of the ion species. In FIG. 11, forexample, the electric field points from the lower electrode toward theupper electrode in the region between electrodes 1180. As a result,positively-charged ions are deflected along an upward trajectory in FIG.11, and negatively-charged ions are deflected along a downwardtrajectory. Ion beams 1162 and 1164 each correspond topositively-charged ion species, with the ion species in ion beam 1162having a larger positive charge than the ion species is beam 1164 (e.g.,due to the larger positive charge of the ions in beam 1162, the beam isdeflected to a greater extent).

Similarly, ion beams 1166 and 1168 each correspond to negatively-chargedion species, with the ion species in ion beam 1168 having a largernegative charge than the ion species in ion beam 1166 (and thereby beingdeflected to a larger extent by the electric field between electrodes1180). Beam 1169 includes neutral particles originally present inparticle stream 1160; the neutral particles are largely unaffected bythe electric field between electrodes 1180, and therefore passundeflected through the electrodes. Each of the separated particlestreams enters one of delivery tubes 1192, 1194, 1196, 1198, and 1199,and can be delivered to an injector system for subsequent accelerationof the particles, or steered to be incident directly on the cellulosicor lignocellulosic material. Alternatively, or in addition, any or allof the separated particle streams can be blocked to prevent ion and/oratomic species from reaching cellulosic or lignocellulosic material. Asyet another alternative, certain particle streams can be combined andthen directed to an injector system and/or steered to be incidentdirectly on the cellulosic or lignocellulosic material using knowntechniques.

In general, particle beam separators can also use magnetic fields inaddition to, or rather than, electric fields for deflecting chargedparticles. In some embodiments, particle beam separators includemultiple pairs of electrodes, where each pair of electrodes generates anelectric field that deflects particles passing therethrough.Alternatively, or in addition, particle beam separators can include oneor more magnetic deflectors that are configured to deflect chargedparticles according to magnitude and sign of the particle charges.

(II) Noble Gas Ions

Noble gas atoms (e.g., helium atoms, neon atoms, argon atoms) formpositively-charged ions when acted upon by relatively strong electricfields. Methods for generating noble gas ions therefore typicallyinclude generating a high-intensity electric field, and then introducingnoble gas atoms into the field region to cause field ionization of thegas atoms. A schematic diagram of a field ionization generator for noblegas ions (and also for other types of ions) is shown in FIG. 12. Fieldionization generator 1200 includes a tapered electrode 1220 positionedwithin a chamber 1210. A vacuum pump 1250 is in fluid communication withthe interior of chamber 1210 via inlet 1240, and reduces the pressure ofbackground gases within chamber 1210 during operation. One or more noblegas atoms 1280 are admitted to chamber 1210 via inlet tube 1230.

During operation, a relatively high positive potential V_(T) (e.g.,positive relative to a common external ground) is applied to taperedelectrode 1220. Noble gas atoms 1280 that enter a region of spacesurrounding the tip of electrode 1220 are ionized by the strong electricfield extending from the tip; the gas atoms lose an electron to the tip,and form positively charged noble gas ions.

The positively charged noble gas ions are accelerated away from the tip,and a certain fraction of the gas ions 1290 pass through extractor 1260and exit chamber 1210, into an ion optical column that includes lens1270, which further deflects and/or focuses the ions.

Electrode 1220 is tapered to increase the magnitude of the localelectric field in the region near the apex of the tip. Depending uponthe sharpness of the taper and the magnitude of potential V_(T), theregion of space in chamber 1210 within which ionization of noble gasatoms occurs can be relatively tightly controlled. As a result, arelatively well collimated beam of noble gas ions 1290 can be obtainedfollowing extractor 1260.

As discussed above in connection with hydrogen ions, the resulting beamof noble gas ions 1290 can be transported through a charged particleoptical column that includes various particle optical elements fordeflecting and/or focusing the noble gas ion beam. The noble gas ionbeam can also pass through an electrostatic and/or magnetic separator,as discussed above in connection with FIG. 11.

Noble gas ions that can be produced in field ionization generator 1200include helium ions, neon ions, argon ions, and krypton ions. Inaddition, field ionization generator 1200 can be used to generate ionsof other gaseous chemical species, including hydrogen, nitrogen, andoxygen.

Noble gas ions may have particular advantages relative to other ionspecies when treating cellulosic or lignocellulosic material. Forexample, while noble gas ions can react with cellulosic orlignocellulosic materials, neutralized noble gas ions (e.g., noble gasatoms) that are produced from such reactions are generally inert, and donot further react with the cellulosic or lignocellulosic material.Moreover, neutral noble gas atoms do not remain embedded in thecellulosic or lignocellulosic material, but instead diffuse out of thematerial. Noble gases are non-toxic and can be used in large quantitieswithout adverse consequences to either human health or the environment.

(III) Carbon, Oxygen, and Nitrogen Ions

Ions of carbon, oxygen, and nitrogen can typically be produced by fieldionization in a system such as field ionization source 1100 or fieldionization generator 1200. For example, oxygen gas molecules and/oroxygen atoms (e.g., produced by heating oxygen gas) can be introducedinto a chamber, where the oxygen molecules and/or atoms are fieldionized to produce oxygen ions. Depending upon the sign of the potentialapplied to the field ionization electrode, positively- and/ornegatively-charged oxygen ions can be produced. The desired ion speciescan be preferentially selected from among various ion species andneutral atoms and molecules by an electrostatic and/or magnetic particleselector, as shown in FIG. 11.

As another example, nitrogen gas molecules can be introduced into thechamber of either field ionization source 1100 or field ionizationgenerator 1200, and ionized to form positively- and/ornegatively-charged nitrogen ions by the relatively strong electric fieldwithin the chamber. The desired ion species can then be separated fromother ionic and neutral species via an electrostatic and/or magneticseparator, as shown in FIG. 11.

To form carbon ions, carbon atoms can be supplied to the chamber ofeither field ionization source 1100 or field ionization generator 1200,wherein the carbon atoms can be ionized to form either positively-and/or negatively-charged carbon ions. The desired ion species can thenbe separated from other ionic and neutral species via an electrostaticand/or magnetic separator, as shown in FIG. 11. The carbon atoms thatare supplied to the chamber of either field ionization source 1100 orfield ionization generator 1200 can be produced by heating acarbon-based target (e.g., a graphite target) to cause thermal emissionof carbon atoms from the target. The target can be placed in relativelyclose proximity to the chamber, so that emitted carbon atoms enter thechamber directly following emission.

(IV) Heavier Ions

Ions of heavier atoms such as sodium and iron can be produced via anumber of methods. For example, in some embodiments, heavy ions such assodium and/or iron ions are produced via thermionic emission from atarget material that includes sodium and/or iron, respectively. Suitabletarget materials include materials such as sodium silicates and/or ironsilicates. The target materials typically include other inert materialssuch as beta-alumina. Some target materials are zeolite materials, andinclude channels formed therein to permit escape of ions from the targetmaterial.

FIG. 13 shows a thermionic emission source 1300 that includes a heatingelement 1310 that contacts a target material 1330, both of which arepositioned inside an evacuated chamber 1305. Heating element 1310 iscontrolled by controller 1320, which regulates the temperature ofheating element 1310 to control the ion current generated from targetmaterial 1330. When sufficient heat is supplied to target material 1330,thermionic emission from the target material generates a stream of ions1340. Ions 1340 can include positively-charged ions of materials such assodium, iron, and other relatively heavy atomic species (e.g., othermetal ions). Ions 1340 can then be collimated, focused, and/or otherwisedeflected by electrostatic and/or magnetic electrodes 1350, which canalso deliver ions 1340 to an injector.

Thermionic emission to form ions of relatively heavy atomic species isalso discussed, for example, in U.S. Pat. No. 4,928,033, entitled“Thermionic Ionization Source,” the entire contents of which areincorporated herein by reference.

In certain embodiments, relatively heavy ions such as sodium ions and/oriron ions can be produced by microwave discharge. FIG. 14 shows aschematic diagram of a microwave discharge source 1400 that producesions from relatively heavy atoms such as sodium and iron. Dischargesource 1400 includes a microwave field generator 1410, a waveguide tube1420, a field concentrator 1430, and an ionization chamber 1490. Duringoperation, field generator 1410 produces a microwave field whichpropagates through waveguide 1420 and concentrator 1430; concentrator1430 increases the field strength by spatially confining the field, asshown in FIG. 14. The microwave field enters ionization chamber 1490. Ina first region inside chamber 1490, a solenoid 1470 produces a strongmagnetic field 1480 in a region of space that also includes themicrowave field. Source 1440 delivers atoms 1450 to this region ofspace. The concentrated microwave field ionizes atoms 1450, and themagnetic field 1480 generated by solenoid 1470 confines the ionizedatoms to form a localized plasma. A portion of the plasma exits chamber1490 as ions 1460. Ions 1460 can then be deflected and/or focused by oneor more electrostatic and/or magnetic elements, and delivered to aninjector.

Atoms 1450 of materials such as sodium and/or iron can be generated bythermal emission from a target material, for example. Suitable targetmaterials include materials such as silicates and other stable salts,including zeolite-based materials. Suitable target materials can alsoinclude metals (e.g., iron), which can be coated on an inert basematerial such as a glass material.

Microwave discharge sources are also discussed, for example, in thefollowing U.S. patents: U.S. Pat. No. 4,409,520, entitled “MicrowaveDischarge Ion Source,” and U.S. Pat. No. 6,396,211, entitled “MicrowaveDischarge Type Electrostatic Accelerator Having Upstream and DownstreamAcceleration Electrodes.” The entire contents of each of the foregoingpatents are incorporated herein by reference.

Particle Beam Sources

Particle beam sources that generate beams for use in irradiatingcellulosic or lignocellulosic material typically include three componentgroups: an injector, which generates or receives ions and introduces theions into an accelerator; an accelerator, which receives ions from theinjector and increases the kinetic energy of the ions; and outputcoupling elements, which manipulate the beam of accelerated ions.

(I) Injectors

Injectors can include, for example, any of the ion sources discussed inthe preceding sections above, which supply a stream of ions forsubsequent acceleration. Injectors can also include various types ofelectrostatic and/or magnetic particle optical elements, includinglenses, deflectors, collimators, filters, and other such elements. Theseelements can be used to condition the ion beam prior to entering theaccelerator; that is, these elements can be used to control thepropagation characteristics of the ions that enter the accelerator.Injectors can also include pre-accelerating electrostatic and/ormagnetic elements that accelerate charged particles to a selected energythreshold prior to entering the accelerator. An example of an injectoris shown in Iwata, Y. et al.

(II) Accelerators

One type of accelerator that can be used to accelerate ions producedusing the sources discussed above is a Dynamitron® (available, forexample, from Radiation Dynamics Inc., now a unit of IBA,Louvain-la-Neuve, Belgium). A schematic diagram of a Dynamitron®accelerator 1500 is shown in FIG. 6 and discussed above.

Another type of accelerator that can be used to accelerate ions fortreatment of cellulosic or lignocellulosic-based material is aRhodotron® accelerator (available, for example, from IBA,Louvain-la-Neuve, Belgium). In general, Rhodotron-type acceleratorsinclude a single recirculating cavity through which ions that are beingaccelerated make multiple passes. As a result, Rhodotron® acceleratorscan be operated in continuous mode at relatively high continuous ioncurrents.

FIG. 15 shows a schematic diagram of a Rhodotron® accelerator 1700.Accelerator 1700 includes an injector 1710, which introduces acceleratedions into recirculating cavity 1720. An electric field source 1730 ispositioned within an inner chamber 1740 of cavity 1720, and generates anoscillating radial electric field. The oscillation frequency of theradial field is selected to match the transit time of injected ionsacross one pass of recirculating cavity 1720. For example, apositively-charged ion is injected into cavity 1720 by injector 1710when the radial electric field in the cavity has zero amplitude. As theion propagates toward chamber 1740, the amplitude of the radial field inchamber 1740 increases to a maximum value, and then decreases again. Theradial field points inward toward chamber 1740, and the ion isaccelerated by the radial field. The ion passes through a hole in thewall of inner chamber 1740, crosses the geometrical center of cavity1720, and passes out through another hole in the wall of inner chamber1740. When the ion is positioned at the enter of cavity 1720, theelectric field amplitude inside cavity 1720 has been reduced to zero (ornearly zero). As the ion emerges from inner chamber 1740, the electricfield amplitude in cavity 1720 begins to increase again, but the fieldis now oriented radially outward. The field magnitude during the secondhalf of the ion's pass through cavity 1720 again reaches a maximum andthen begins to diminish. As a result, the positive ion is againaccelerated by the electric field as the ion completes the second halfof a first pass through cavity 1720.

Upon reaching the wall of cavity 1720, the magnitude of the electricfield in cavity 1720 is zero (or nearly zero) and the ion passes throughan aperture in the wall and encounters one of beam deflection magnets1750. The beam deflection magnets essentially reverse the trajectory ofthe ion, as shown in FIG. 15, directing the ion to re-enter cavity 1720through another aperture in the wall of the chamber. When the ionre-enters cavity 1720, the electric field therein begins to increase inamplitude again, but is now once more oriented radially inward. Thesecond and subsequent passes of the ion through cavity 1720 follow asimilar pattern, so that the orientation of the electric field alwaysmatches the direction of motion of the ion, and the ion is acceleratedon every pass (and every half-pass) through cavity 1720.

As shown in FIG. 15, after six passes through cavity 1720, theaccelerated ion is coupled out of cavity 1720 as a portion ofaccelerated ion beam 1760. The accelerated ion beam passes through oneor more electrostatic and/or magnetic particle optical elements 1770,which can include lenses, collimators, beam deflectors, filters, andother optical elements. For example, under control of an external logicunit, elements 1770 can include an electrostatic and/or magneticdeflector that sweeps accelerated beam 1760 across a two-dimensionalplanar region oriented perpendicular to the direction of propagation ofbeam 1760.

Ions that are injected into cavity 1720 are accelerated on each passthrough cavity 1720. In general, therefore, to obtain accelerated beamshaving different average ion energies, accelerator 1700 can include morethan one output coupling. For example, in some embodiments, one or moreof deflection magnets 1750 can be modified to allow a portion of theions reaching the magnets to be coupled out of accelerator 1700, and aportion of the ions to be returned to chamber 1720. Multiple acceleratedoutput beams can therefore be obtained from accelerator 1700, each beamcorresponding to an average ion energy that is related to the number ofpasses through cavity 1720 for the ions in the beam.

Accelerator 1700 includes 5 deflection magnets 1750, and ions injectedinto cavity 1720 make 6 passes through the cavity. In general, however,accelerator 1700 can include any number of deflection magnets, and ionsinjected into cavity 1720 can make any corresponding number of passesthrough the cavity. For example, in some embodiments, accelerator 1700can include at least 6 deflection magnets and ions can make at least 7passes through the cavity (e.g., at least 7 deflection magnets and 8passes through the cavity, at least 8 deflection magnets and 9 passesthrough the cavity, at least 9 deflection magnets and 10 passes throughthe cavity, at least 10 deflection magnets and 11 passes through thecavity).

Typically, the electric field generated by field source 1730 provides asingle-cavity-pass gain of about 1 MeV to an injected ion. In general,however, higher single-pass gains are possible by providing ahigher-amplitude electric field within cavity 1720. In some embodiments,for example, the single-cavity-pass gain is about 1.2 MeV or more (e.g.,1.3 MeV or more, 1.4 MeV or more, 1.5 MeV or more, 1.6 MeV or more, 1.8MeV or more, 2.0 MeV or more, 2.5 MeV or more).

The single-cavity-pass gain also depends upon the magnitude of thecharge carried by the injected ion. For example, ions bearing multiplecharges will experience higher single-pass-cavity gain than ions bearingsingle charges, for the same electric field within cavity. As a result,the single-pass-cavity gain of accelerator 1700 can be further increasedby injecting ions having multiple charges.

In the foregoing description of accelerator 1700, a positively-chargedion was injected into cavity 1720. Accelerator 1700 can also acceleratenegatively charged ions. To do so, the negatively charged ions areinjected so that the direction of their trajectories is out of phasewith the radial electric field direction. That is, the negativelycharged ions are injected so that on each half pass through cavity 1720,the direction of the trajectory of each ion is opposite to the directionof the radial electric field. Achieving this involves simply adjustingthe time at which negatively-charged ions are injected into cavity 1720.Accordingly, accelerator 1700 is capable of simultaneously acceleratingions having the same approximate mass, but opposite charges. Moregenerally, accelerator 1700 is capable of simultaneously acceleratingdifferent types of both positively- and negatively-charged (and bothsingly- and multiply-charged) ions, provided that the transit times ofthe ions across cavity 1720 are relatively similar. In some embodiments,accelerator 1700 can include multiple output couplings, providingdifferent types of accelerated ion beams having similar or differentenergies.

Other types of accelerators can also be used to accelerate ions forirradiation of cellulosic or lignocellulosic material. For example, insome embodiments, ions can be accelerated to relatively high averageenergies in cyclotron- and/or synchrotron-based accelerators. Theconstruction and operation of such accelerators is well-known in theart. As another example, in some embodiments, Penning-type ion sourcescan be used to generate and/or accelerate ions for treating cellulosicor lignocellulosic-based material. The design of Penning-type sources isdiscussed in section 7.2.1 of Prelec (1997).

Static and/or dynamic accelerators of various types can also generallybe used to accelerate ions. Static accelerators typically include aplurality of electrostatic lenses that are maintained at different DCvoltages. By selecting appropriate values of the voltages applied toeach of the lens elements, ions introduced into the accelerator can beaccelerated to a selected final energy. FIG. 16 shows a simplifiedschematic diagram of a static accelerator 1800 that is configured toaccelerate ions to treat cellulosic or lignocellulosic material 1835.Accelerator 1800 includes an ion source 1810 that produces ions andintroduces the ions into an ion column 1820. Ion column 1820 includes aplurality of electrostatic lenses 1825 that accelerate the ionsgenerated by ion source 1810 to produce an ion beam 1815. DC voltagesare applied to lenses 1825; the potentials of the lenses remainapproximately constant during operation. Generally, the electricalpotential within each lens is constant, and the ions of ion beam 1815are accelerated in the gaps between the various lenses 1825. Ion column1820 also includes a deflection lens 1830 and a collimation lens 1832.These two lenses operate to direct ion beam 1815 to a selected positionon cellulosic or lignocellulosic material 1835, and to focus ion beam1815 onto the cellulosic or lignocellulosic material.

Although FIG. 16 shows a particular embodiment of a static accelerator,many other variations are possible and suitable for treating cellulosicor lignocellulosic material. In some embodiments, for example, therelative positions of deflection lens 1830 and collimation lens 1832along ion column 1820 can be exchanged. Additional electrostatic lensescan also be present in ion column 1820, and ion column 1820 can furtherinclude magnetostatic optical elements. In certain embodiments, a widevariety of additional elements can be present in ion column 1820,including deflectors (e.g., quadrupole, hexapole, and/or octopoledeflectors), filtering elements such as apertures to remove undesiredspecies (e.g., neutrals and/or certain ionic species) from ion beam1815, extractors (e.g., to establish a spatial profile for ion beam1815), and other electrostatic and/or magnetostatic elements.

Dynamic linear accelerators—often referred to as LINACS—can also be usedto generate an ion beam that can be used to treat cellulosic orlignocellulosic material. Typically, dynamic linear accelerators includean ion column with a linear series of radiofrequency cavities, each ofwhich produces an intense, oscillating radiofrequency (RF) field that istimed to coincide with injection and propagation of ions into the ioncolumn. As an example, devices such as klystrons can be used togenerated the RF fields in the cavities. By matching the fieldoscillations to the injection times of ions, the RF cavities canaccelerate ions to high energies without having to maintain peakpotentials for long periods of time. As a result, LINACS typically donot have the same shielding requirements as DC accelerators, and aretypically shorter in length. LINACS typically operate at frequencies of3 GHz (S-band, typically limited to relatively low power) and 1 GHz(L-band, capable of significantly higher power operation). TypicalLINACS have an overall length of 2-4 meters.

A schematic diagram of a dynamic linear accelerator 1850 (e.g., a LINAC)is shown in FIG. 17. LINAC 1850 includes an ion source 1810 and an ioncolumn 1855 that includes three acceleration cavities 1860, a deflector1865, and a focusing lens 1870. Deflector 1865 and focusing lens 1870function to steer and focus ion beam 1815 onto cellulosic orlignocellulosic material 1835 following acceleration, as discussedabove. Acceleration cavities 1860 are formed of a conductive materialsuch as copper, and function as a waveguide for the accelerated ions.Klystrons 1862, connected to each of cavities 1860, generate the dynamicRF fields that accelerate the ions within the cavities. Klystrons 1862are individually configured to produce RF fields that, together,accelerate the ions in ion beam 1815 to a final, selected energy priorto being incident on cellulosic or lignocellulosic material 1835.

As discussed above in connection with static accelerators, manyvariations of dynamic accelerator 1850 are possible and can be used toproduce an ion beam for treating cellulosic or lignocellulosic material.For example, in some embodiments, additional electrostatic lenses canalso be present in ion column 1855, and ion column 1855 can furtherinclude magnetostatic optical elements. In certain embodiments, a widevariety of additional elements can be present in ion column 1855,including deflectors (e.g., quadrupole, hexapole, and/or octopoledeflectors), filtering elements such as apertures to remove undesiredspecies (e.g., neutrals and/or certain ionic species) from ion beam1815, extractors (e.g., to establish a spatial profile for ion beam1815), and other electrostatic and/or magnetostatic elements. Inaddition to the specific static and dynamic accelerators discussedabove, other suitable accelerator systems include, for example: DCinsulated core transformer (ICT) type systems, available from NissinHigh Voltage, Japan; S-band LINACS, available from L3-PSD (USA), LinacSystems (France), Mevex (Canada), and Mitsubishi Heavy Industries(Japan); L-band LINACS, available from Iotron Industries (Canada); andILU-based accelerators, available from Budker Laboratories (Russia).

In some embodiments, van de Graaff-based accelerators can be used toproduce and/or accelerate ions for subsequent treatment of cellulosic orlignocellulosic material. FIG. 18 shows an embodiment of a van de Graaffaccelerator 1900 that includes a spherical shell electrode 1902 and aninsulating belt 1906 that recirculates between electrode 1902 and a base1904 of accelerator 1900. During operation, insulating belt 1906 travelsover pulleys 1910 and 1908 in the direction shown by arrow 1918, andcarries charge into electrode 1902. Charge is removed from belt 1906 andtransferred to electrode 1902, so that the magnitude of the electricalpotential on electrode 1902 increases until electrode 1902 is dischargedby a spark (or, alternatively, until the charging current is balanced bya load current).

Pulley 1910 is grounded, as shown in FIG. 18. A corona discharge ismaintained between a series of points or a fine wire on one side of belt1906. Wire 1914 is configured to maintain the corona discharge inaccelerator 1900. Wire 1914 is maintained at a positive potential, sothat belt 1906 intercepts positive ions moving from wire 1914 to pulley1910. As belt 1906 moves in the direction of arrow 1918, the interceptedcharges are carried into electrode 1902, where they are removed frombelt 1906 by a needle point 1916 and transferred to electrode 1902. As aresult, positive charges accumulate on the surface of electrode 1902;these charges can be discharged from the surface of electrode 1902 andused to treat cellulosic or lignocellulosic material. In someembodiments, accelerator 1900 can be configured to provide negativelycharged ions by operating wire 1914 and needle point 1916 at a negativepotential with respect to grounded pulley 1910.

In general, accelerator 1900 can be configured to provide a wide varietyof different types of positive and negative charges for treatingcellulosic or lignocellulosic material. Exemplary types of chargesinclude electrons, protons, hydrogen ions, carbon ions, oxygen ions,halogen ions, metal ions, and other types of ions.

In certain embodiments, tandem accelerators (including folded tandemaccelerators) can be used to generate ion beams for treatment ofcellulosic or lignocellulosic material. An example of a folded tandemaccelerator 1950 is shown in FIG. 19. Accelerator 1950 includes anaccelerating column 1954, a charge stripper 1956, a beam deflector 1958,and an ion source 1952.

During operation, ion source 1952 produces a beam 1960 of negativelycharged ions, which is directed to enter accelerator 1950 through inputport 1964. In general, ion source 1952 can be any type of ion sourcethat produces negatively charged ions. For example, suitable ion sourcesinclude a source of negative ions by cesium sputtering (SNICS) source, aRF-charge exchange ion source, or a toroidal volume ion source (TORVIS).Each of the foregoing exemplary ion sources is available, for example,from National Electrostatics Corporation (Middleton, Wis.).

Once inside accelerator 1950, the negative ions in beam 1960 areaccelerated by accelerating column 1954. Typically, accelerating column1954 includes a plurality of accelerating elements such as electrostaticlenses. The potential difference applied in column 1954 to acceleratethe negative ions can be generated using various types of devices. Forexample, in some embodiments, (e.g., Pelletron® accelerators), thepotential is generated using a Pelletron® charging device. Pelletron®devices include a charge-carrying belt that is formed from a pluralityof metal (e.g., steel) chain links or pellets that are bridged byinsulating connectors (e.g., formed from a material such as nylon).During operation, the belt recirculates between a pair of pulleys, oneof which is maintained at ground potential. As the belt moves betweenthe grounded pulley and the opposite pulley (e.g., the terminal pulley),the metal pellets are positively charged by induction. Upon reaching theterminal pulley, the positive charge that has accumulated on the belt isremoved, and the pellets are negatively charged as they leave theterminal pulley and return to the ground pulley.

The Pelletron® device generates a large positive potential within column1954 that is used to accelerate the negative ions of beam 1960. Afterundergoing acceleration in column 1954, beam 1960 passes through chargestripper 1956. Charge stripper 1956 can be implemented as a thin metalfoil and/or a tube containing a gas that strips electrons from thenegative ions, for example. The negatively charged ions are therebyconverted to positively charged ions, which emerge from charge stripper1956. The trajectories of the emerging positively charged ions arealtered so that the positively charged ions travel back throughaccelerating column 1954, undergoing a second acceleration in the columnbefore emerging as positively charged ion beam 1962 from output port1966. Positively charged ion beam 1962 can then be used to treatcellulosic or lignocellulosic material according to the various methodsdisclosed herein.

Due to the folded geometry of accelerator 1950, ions are accelerated toa kinetic energy that corresponds to twice the potential differencegenerated by the Pelletron® charging device. For example, in a 2 MVPelletron® accelerator, hydride ions that are introduced by ion source1952 will be accelerated to an intermediate energy of 2 MeV during thefirst pass through column 1954, converted to positive ions (e.g.,protons), and accelerated to a final energy of 4 MeV during the secondpass through column 1954.

In certain embodiments, column 1954 can include elements in addition to,or as alternatives to, the Pelletron® charging device. For example,column 1954 can include static accelerating elements (e.g., DCelectrodes) and/or dynamic acceleration cavities (e.g., LINAC-typecavities with pulse RF field generators for particle acceleration).Potentials applied to the various accelerating devices are selected toaccelerate the negatively charged ions of beam 1960.

Exemplary tandem accelerators, including both folded and non-foldedaccelerators, are available from National Electrostatics Corporation(Middleton, Wis.), for example.

In some embodiments, combinations of two or more of the various types ofaccelerators can be used to produce ion beams that are suitable fortreating cellulosic or lignocellulosic material. For example, a foldedtandem accelerator can be used in combination with a linear accelerator,a Rhodotron® accelerator, a Dynamitron®, a static accelerator, or anyother type of accelerator to produce ion beams. Accelerators can be usedin series, with the output ion beam from one type of acceleratordirected to enter another type of accelerator for additionalacceleration. Alternatively, multiple accelerators can be used inparallel to generate multiple ion beams. In certain embodiments,multiple accelerators of the same type can be used in parallel and/or inseries to generate accelerated ion beams.

In some embodiments, multiple similar and/or different accelerators canbe used to generate ion beams having different compositions. Forexample, a first accelerator can be used to generate one type of ionbeam, while a second accelerator can be used to generate a second typeof ion beam. The two ion beams can then each be further accelerated inanother accelerator, or can be used to treat cellulosic orlignocellulosic material.

Further, in certain embodiments, a single accelerator can be used togenerate multiple ion beams for treating cellulosic or lignocellulosicmaterial. For example, any of the accelerators discussed herein (andother types of accelerators as well) can be modified to produce multipleoutput ion beams by sub-dividing an initial ion current introduced intothe accelerator from an ion source. Alternatively, or in addition, anyone ion beam produced by any of the accelerators disclosed herein caninclude only a single type of ion, or multiple different types of ions.

In general, where multiple different accelerators are used to produceone or more ion beams for treatment of cellulosic or lignocellulosicmaterial, the multiple different accelerators can be positioned in anyorder with respect to one another. This provides for great flexibilityin producing one or more ion beams, each of which has carefully selectedproperties for treating cellulosic or lignocellulosic material (e.g.,for treating different components in cellulosic or lignocellulosicmaterial).

The ion accelerators disclosed herein can also be used in combinationwith any of the other treatment steps disclosed herein. For example, insome embodiments, electrons and ions can be used in combination to treatcellulosic or lignocellulosic material. The electrons and ions can beproduced and/or accelerated separately, and used to treat cellulosic orlignocellulosic material sequentially (in any order) and/orsimultaneously. In certain embodiments, electron and ion beams can beproduced in a common accelerator and used to treat cellulosic orlignocellulosic material. For example, many of the ion acceleratorsdisclosed herein can be configured to produce electron beams as analternative to, or in addition to, ion beams. For example, Dynamitron®accelerators, Rhodotron® accelerators, and LINACs can be configured toproduce electron beams for treatment of cellulosic or lignocellulosicmaterial.

Moreover, treatment of cellulosic or lignocellulosic material with ionbeams can be combined with other techniques such as sonication. Ingeneral, sonication-based treatment can occur before, during, or afterion-based treatment. Other treatments such as electron beam treatmentcan also occur in any combination and/or order with ultrasonic treatmentand ion beam treatment.

Paper Additives

Any of the many additives and coatings used in the papermaking industrycan be added to or applied to the fibrous materials, papers, or anyother materials and products described herein. Additives include fillerssuch as calcium carbonate, plastic pigments, graphite, wollastonite,mica, glass, fiber glass, silica, and talc; inorganic flame retardantssuch as alumina trihydrate or magnesium hydroxide; organic flameretardants such as chlorinated or brominated organic compounds; carbonfibers; and metal fibers or powders (e.g., aluminum, stainless steel).These additives can reinforce, extend, or change electrical ormechanical properties, compatibility properties, or other properties.Other additives include starch, lignin, fragrances, coupling agents,antioxidants, opacifiers, heat stabilizers, colorants such as dyes andpigments, polymers, e.g., degradable polymers, photostabilizers, andbiocides. Representative degradable polymers include polyhydroxy acids,e.g., polylactides, polyglycolides and copolymers of lactic acid andglycolic acid, poly(hydroxybutyric acid), poly(hydroxyvaleric acid),poly[lactide-co-(e-caprolactone)], poly[glycolide-co-(e-caprolactone)],polycarbonates, poly(amino acids), poly(hydroxyalkanoate)s,polyanhydrides, polyorthoesters and blends of these polymers. Whenadditives are included, they can be present in amounts, calculated on adry weight basis, of from below about 1 percent to as high as about 80percent, based on total weight of the fibrous material. More typically,amounts range from between about 0.5 percent to about 50 percent byweight, e.g., from about 0.5 percent to about 5 percent, 10 percent, 20percent, 30, percent or more, e.g., 40 percent.

Any additives described herein can be encapsulated, e.g., spray dried ormicroencapsulated, e.g., to protect the additives from heat or moistureduring handling.

Suitable coatings include any of the many coatings used in the paperindustry to provide specific surface characteristics, includingperformance characteristics required for particular printingapplications.

As mentioned above, various fillers can be included in the paper. Forexample, inorganic fillers such as calcium carbonate (e.g., precipitatedcalcium carbonate or natural calcium carbonate), aragonite clay,orthorhombic clays, calcite clay, rhombohedral clays, kaolin clay,bentonite clay, dicalcium phosphate, tricalcium phosphate, calciumpyrophosphate, insoluble sodium metaphosphate, precipitated calciumcarbonate, magnesium orthophosphate, trimagnesium phosphate,hydroxyapatites, synthetic apatites, alumina, silica xerogel, metalaluminosilicate complexes, sodium aluminum silicates, zirconiumsilicate, silicon dioxide or combinations of the inorganic additives maybe used. The fillers can have, e.g., a particle size of greater than 1micron, e.g., greater than 2, 5, 10, or 25 microns or even greater than35 microns.

Nanometer scale fillers can also be used alone, or in combination withfibrous materials of any size and/or shape. The fillers can be in theform of, e.g., particles, plates or fibers. For example, nanometer sizedclays, silicon and carbon nanotubes, and silicon and carbon nanowirescan be used. The fillers can have a transverse dimension less than 1000nm, e.g., less than 900, 800, 750, 600, 500, 350, 300, 250, 200, or 100nm, or even less than 50 nm.

In some embodiments, the nano-clay is a montmorillonite. Such clays areavailable from Nanocor, Inc. and Southern Clay products, and have beendescribed in U.S. Pat. Nos. 6,849,680 and 6,737,464. The clays can besurface treated before mixing into, e.g., a resin or a fibrous material.For example, the clay can be surface treated so that its surface isionic in nature, e.g., cationic or anionic.

Aggregated or agglomerated nanometer scale fillers, or nanometer scalefillers that are assembled into supramolecular structures, e.g.,self-assembled supramolecular structures can also be used. Theaggregated or supramolecular fillers can be open or closed in structure,and can have a variety of shapes, e.g., cage, tube or spherical.

Lignin Content

Paper can contain lignin, for example up to 1, 2, 3, 4, 5, 7.5, 10, 15,20, or even 25% by weight of lignin.

This lignin content can be the result of the lignin present in thelignocellulosic material(s) used to manufacture the paper.Alternatively, or in addition, lignin can be added to the paper as anadditive, as mentioned above. In this case, the lignin can be added as asolid, e.g., as a powder or other particulate material, or can bedissolved or dispersed and added in liquid form. In the latter case, thelignin can be dissolved in solvent or a solvent system. The solvent orsolvent system can be in the form of a single phase or two or morephases. Solvent systems for cellulosic and lignocellulosic materialsinclude DMSO-salt systems. Such systems include, for example, DMSO incombination with a lithium, magnesium, potassium, sodium or zinc salt.Lithium salts include LiCl, LiBr, LiI, lithium perchlorate and lithiumnitrate. Magnesium salts include magnesium nitrate and magnesiumchloride. Potassium salts include potassium iodide and nitrate. Examplesof sodium salts include sodium iodide and nitrate. Examples of zincsalts include zinc chloride and nitrate. Any salt can be anhydrous orhydrated. Typical loadings of the salt in the DMSO are between about 1and about 50 percent, e.g., between about 2 and 25, between about 3 and15 or between about 4 and 12.5 percent by weight.

In some cases, lignin will cross-link in the paper during irradiation,further enhancing the physical properties of the paper.

Paper Types

Paper is often characterized by weight. The weight assigned to a paperis the weight of a ream, 500 sheets, of varying “basic sizes,” beforethe paper is cut into the size as sold to end customers. For example, aream of 20 lb, 8½×11″ paper weighs 5 pounds, because it has been cutfrom a larger sheet into four pieces. In the United States, printingpaper is generally 20 lb, 24 lb, or 32 lb at most. Cover stock isgenerally 68 lb, and 110 lb or more.

In Europe the weight is expressed in grams per square meter (gsm or justg). Printing paper is generally between 60 g and 120 g. Anything heavierthan 160 g is considered card stock. The weight of a ream thereforedepends on the dimensions of the paper, e.g., one ream of A4 (210 mm×297mm) size (approx 8.27″×11.7″) weighs 2.5 kilograms (approx 5.5 pounds).

The density of paper ranges from 250 kg/m³ (16 lb/ft³) for tissue paperto 1500 kg/m3 (94 lb/ft³) for some specialty paper. In some cases thedensity of printing paper is about 800 kg/m³ (50 lb/ft³).

The processes described herein are suitable for use with all of thesegrades of paper, as well as other types of paper such as corrugatedcardboard, paper board, and other paper products. The processesdescribed herein may be used to treat paper that is used, for example,in any of the following applications: as stamps; as paper money, banknotes, securities, checks, and the like; in books, magazines,newspapers, and art; for packaging, e.g., paper board, corrugatedcardboard, paper bags, envelopes, wrapping tissue, boxes; in householdproducts such as toilet paper, tissues, paper towel sand paper napkins;paper honeycomb, used as a core material in composite materials;building materials; construction paper; disposable clothing; and invarious industrial uses including emery paper, sandpaper, blottingpaper, litmus paper, universal indicator paper, paper chromatography,battery separators, and capacitor dielectrics. The paper may be singleor multi-layered paper.

The paper may be made of any desired type of fiber, including fiberderived from wood and recycled paper, as well as fiber derived fromother sources. Vegetable fiber materials, such as cotton, hemp, linen,and rice, can be used alone or in combination with each other or withwood-derived fibers. Other non-wood fiber sources include, but are notlimited to, sugarcane, bagasse, straw, bamboo, kenaf, jute, flax, andcotton. A wide variety of synthetic fibers, such as polypropylene andpolyethylene, as well as other ingredients such as inorganic fillers,may be incorporated into paper as a means for imparting desirablephysical properties. It may be desirable to include these non-woodfibers in paper used in special application such as for paper money,fine stationary, art paper and other applications requiring particularstrength or aesthetic characteristics.

The paper may be irradiated before or after printing. Radiation may beused to mark the paper, for example by increasing the number ofcarboxylic acid groups in the irradiated area. This may be useful, forexample, in marking currency.

Process Water

In the processes disclosed herein, whenever water is used in anyprocess, it may be grey water, e.g., municipal grey water, or blackwater. In some embodiments, the grey or black water is sterilized priorto use. Sterilization may be accomplished by any desired technique, forexample by irradiation, steam, or chemical sterilization.

EXAMPLES

The following examples are not intended to limit the inventions recitedin the claims.

Example 1—Methods of Determining Molecular Weight of Cellulosic andLignocellulosic Materials by Gel Permeation Chromatography

This example illustrates how molecular weight is determined for thematerials discussed herein. Cellulosic and lignocellulosic materials foranalysis were treated as follows:

A 1500 pound skid of virgin bleached white Kraft board having a bulkdensity of 30 lb/ft³ was obtained from International Paper. The materialwas folded flat, and then fed into a 3 hp Flinch Baugh shredder at arate of approximately 15 to 20 pounds per hour. The shredder wasequipped with two 12 inch rotary blades, two fixed blades and a 0.30inch discharge screen. The gap between the rotary and fixed blades wasadjusted to 0.10 inch. The output from the shredder resembled confetti(as above). The confetti-like material was fed to a Munson rotary knifecutter, Model SC30. The discharge screen had ⅛ inch openings. The gapbetween the rotary and fixed blades was set to approximately 0.020 inch.The rotary knife cutter sheared the confetti-like pieces across theknife-edges. The material resulting from the first shearing was fed backinto the same setup and the screen was replaced with a 1/16 inch screen.This material was sheared. The material resulting from the secondshearing was fed back into the same setup and the screen was replacedwith a 1/32 inch screen. This material was sheared. The resultingfibrous material had a BET surface area of 1.6897 m²/g+/−0.0155 m²/g, aporosity of 87.7163 percent and a bulk density (@0.53 psia) of 0.1448g/mL. An average length of the fibers was 0.824 mm and an average widthof the fibers was 0.0262 mm, giving an average L/D of 32:1.

Sample materials presented in the following Tables 1 and 2 include Kraftpaper (P), wheat straw (WS), alfalfa (A), and switchgrass (SG). Thenumber “132” of the Sample ID refers to the particle size of thematerial after shearing through a 1/32 inch screen. The number after thedash refers to the dosage of radiation (MRad) and “US” refers toultrasonic treatment. For example, a sample ID “P132-10” refers to Kraftpaper that has been sheared to a particle size of 132 mesh and has beenirradiated with 10 MRad.

TABLE 1 Peak Average Molecular Weight of Irradiated Kraft Paper SampleDosage¹ Average MW ± Source Sample ID (MRad) Ultrasound² Std Dev. KraftP132 0 No 32853 ± 10006 Paper P132-10 10 No  61398 ± 2468** P132-100 100No 8444 ± 580  P132-181 181 No 6668 ± 77  P132-US 0 Yes 3095 ± 1013**Low doses of radiation appear to increase the molecular weight of somematerials ¹Dosage Rate = 1 MRad/hour ²Treatment for 30 minutes with 20kHz ultrasound using a 1000 W horn under re-circulating conditions withthe material dispersed in water.

TABLE 2 Peak Average Molecular Weight of Irradiated Materials Dosage¹Average MW ± Sample ID Peak # (MRad) Ultrasound² Std Dev. WS132 1 0 No1407411 ± 175191 2 0 No 39145 ± 3425 3 0 No 2886 ± 177 WS132-10* 1 10 No26040 ± 3240 WS132-100* 1 100 No 23620 ± 453  A132 1 0 No 1604886 ±151701 2 0 No 37525 ± 3751 3 0 No 2853 ± 490 A132-10* 1 10 No 50853 ±1665 2 10 No 2461 ± 17  A132-100* 1 100 No 38291 ± 2235 2 100 No 2487 ±15  SG132 1 0 No 1557360 ± 83693  2 0 No 42594 ± 4414 3 0 No 3268 ± 249SG132-10* 1 10 No 60888 ± 9131 SG132-100* 1 100 No 22345 ± 3797SG132-10-US 1 10 Yes  86086 ± 43518 2 10 Yes 2247 ± 468 SG132-100-US 1100 Yes  4696 ± 1465 *Peaks coalesce after treatment **Low doses ofradiation appear to increase the molecular weight of some materials¹Dosage Rate = 1 MRad/hour ²Treatment for 30 minutes with 20 kHzultrasound using a 1000 W horn under re-circulating conditions with thematerial dispersed in water.

Gel Permeation Chromatography (GPC) is used to determine the molecularweight distribution of polymers. During GPC analysis, a solution of thepolymer sample is passed through a column packed with a porous geltrapping small molecules. The sample is separated based on molecularsize with larger molecules eluting sooner than smaller molecules. Theretention time of each component is most often detected by refractiveindex (RI), evaporative light scattering (ELS), or ultraviolet (UV) andcompared to a calibration curve. The resulting data is then used tocalculate the molecular weight distribution for the sample.

A distribution of molecular weights rather than a unique molecularweight is used to characterize synthetic polymers. To characterize thisdistribution, statistical averages are utilized. The most common ofthese averages are the “number average molecular weight” (M_(n)) and the“weight average molecular weight” (M_(w)). Methods of calculating thesevalues are described in the art, e.g., in Example 9 of WO 2008/073186.

The polydispersity index or PI is defined as the ratio of M_(w)/M_(n).The larger the PI, the broader or more disperse the distribution. Thelowest value that a PI can be is 1. This represents a monodispersesample; that is, a polymer with all of the molecules in the distributionbeing the same molecular weight.

The peak molecular weight value (M_(P)) is another descriptor defined asthe mode of the molecular weight distribution. It signifies themolecular weight that is most abundant in the distribution. This valuealso gives insight to the molecular weight distribution.

Most GPC measurements are made relative to a different polymer standard.The accuracy of the results depends on how closely the characteristicsof the polymer being analyzed match those of the standard used. Theexpected error in reproducibility between different series ofdeterminations, calibrated separately, is about 5-10% and ischaracteristic to the limited precision of GPC determinations.Therefore, GPC results are most useful when a comparison between themolecular weight distribution of different samples is made during thesame series of determinations.

The lignocellulosic samples required sample preparation prior to GPCanalysis. First, a saturated solution (8.4% by weight) of lithiumchloride (LiCl) was prepared in dimethyl acetamide (DMAc). Approximately100 mg of the sample was added to approximately 10 g of a freshlyprepared saturated LiCl/DMAc solution, and the mixture was heated toapproximately 150° C.−170° C. with stirring for 1 hour. The resultingsolutions were generally light- to dark-yellow in color. The temperatureof the solutions were decreased to approximately 100° C. and heated foran additional 2 hours. The temperature of the solutions were thendecreased to approximately 50° C. and the sample solution was heated forapproximately 48 to 60 hours. Of note, samples irradiated at 100 MRadwere more easily solubilized as compared to their untreated counterpart.Additionally, the sheared samples (denoted by the number 132) hadslightly lower average molecular weights as compared with uncut samples.

The resulting sample solutions were diluted 1:1 using DMAc as solventand were filtered through a 0.45 μm PTFE filter. The filtered samplesolutions were then analyzed by GPC. The peak average molecular weight(Mp) of the samples, as determined by Gel Permeation Chromatography(GPC), are summarized in Tables 1 and 2, above. Each sample was preparedin duplicate and each preparation of the sample was analyzed induplicate (two injections) for a total of four injections per sample.The EasiCal® polystyrene standards PS1A and PS1B were used to generate acalibration curve for the molecular weight scale from about 580 to7,500,00 Daltons. GPC analysis conditions are recited in Table 3, below.

TABLE 3 GPC Analysis Conditions Instrument: Waters Alliance GPC 2000Plgel 10μ Mixed-B Columns (3): S/N's: 10M-MB-148-83; 10M-MB-148-84;10M-MB-174-129 Mobile Phase (solvent): 0.5% LiCl in DMAc (1.0 mL/min.)Column/Detector 70° C. Temperature: Injector Temperature: 70° C. SampleLoop Size: 323.5 μL

Example 2—Electron Beam Processing Cardboard Samples

Brown cardboard samples 0.050 inches thick were treated with a beam ofelectrons using a vaulted Rhodotron® TT200 continuous wave acceleratordelivering 5 MeV electrons at 80 kW output power. Table 4 describes thenominal parameters for the TT200. Table 5 reports the nominal doses (inMRad) and actual doses (in kgy) delivered to the samples.

TABLE 4 Rhodotron ® TT 200 Parameters Beam Beam Produced: Acceleratedelectrons Beam energy: Nominal (maximum): 10 MeV (+0 keV-250 keV Energydispersion at 10 Mev: Full width half maximum (FWHM) 300 keV Beam powerat 10 MeV: Guaranteed Operating Range 1 to 80 kW Power ConsumptionStand-by condition <15 kW (vacuum and cooling ON): At 50 kW beam power:<210 kW At 80 kW beam power: <260 kW RF System Frequency: 107.5 ± 1 MHzTetrode type: Thomson TH781 Scanning Horn Nominal Scanning Length 120 cm(measured at 25-35 cm from window): Scanning Range: From 30% to 100% ofNominal Scanning Length Nominal Scanning Frequency 100 Hz ± 5%   (atmax. scanning length): Scanning Uniformity ±5% (across 90% of NominalScanning Length)

TABLE 5 Dosages Delivered to Samples Total Dosage (MRad) (NumberAssociated with Sample ID Delivered Dose (kgy)¹ 1 9.9 3 29.0 5 50.4 769.2 10 100.0 15 150.3 20 198.3 30 330.9 50 529.0 70 695.9 100 993.6¹For example, 9.9 kgy was delivered in 11 seconds at a beam current of 5mA and a line speed of 12.9 feet/minute. Cool time between 1 MRadtreatments was about 2 minutes.

The cardboard samples treated below 7 MRad were stiffer to the touchthan untreated controls, but otherwise appeared visibly identical to thecontrols. Samples treated at about 10 MRad were of comparable stiffnessto the controls to the touch, while those treated with higher doses weremore flexible under manipulation. Extensive material degradation wasvisibly apparent for samples treated above 50 Mrad.

OTHER EMBODIMENTS

It is to be understood that while the invention has been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Otheraspects, advantages, and modifications are within the scope of thefollowing claims.

What is claimed is:
 1. A method of treating paper, the methodcomprising: directing positively charged ions to be incident on paperhaving a paper weight between 20 lb and 32 lb, the positively chargedions having been provided by forming a plurality of negatively chargedions, accelerating the negatively charged ions to a first energy,removing a plurality of electrons from at least some of the negativelycharged ions to form positively charged ions, and accelerating thepositively charged ions to a second energy.
 2. The method of claim 1wherein the paper has a density between 250 kg/m³ and 1500 kg/m³.
 3. Themethod of claim 1 wherein the paper comprises printing paper.
 4. Themethod of claim 1 wherein the paper comprises recycled paper.
 5. Themethod of claim 1 wherein the positively charged ions have an energy ofabout 4 MeV.
 6. The method of claim 1 further comprising forming thepositively charged ions in a folded tandem accelerator.
 7. The method ofclaim 1 wherein the ions are selected from the group consisting ofhydrogen ions, carbon ions, oxygen ions, halogen ions, and metal ions.